[PATCH v2] Add CONTRIBUTING.md

[Yumei Huang <yuhuang@redhat.com>]

Signed-off-by: Yumei Huang <yuhuang@redhat.com>
---
 CONTRIBUTING.md | 152 ++++++++++++++++++++++++++++++++++++++++++++++++
 README.md       |   6 +-
 2 files changed, 156 insertions(+), 2 deletions(-)
 create mode 100644 CONTRIBUTING.md

diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
new file mode 100644
index 0000000..13fba69
--- /dev/null
+++ b/CONTRIBUTING.md
@@ -0,0 +1,152 @@
+<!---
+SPDX-License-Identifier: GPL-2.0-or-later
+Copyright (c) 2025 Red Hat GmbH
+Author: Yumei Huang <yuhuang@redhat.com>
+-->
+
+# Contributing to passt
+
+Thank you for your interest in contributing! This document explains how
+to prepare patches and participate in the email-based review process.
+
+## Workflow
+
+### 1. Clone the project
+
+    git clone git://passt.top/passt
+
+
+### 3. Make Changes and Commit
+
+* You can decide to work on the master branch or a separate branch as below:
+
+        cd passt
+        git checkout -b my-feature-branch
+
+* Edit the source code or documentation following the [Linux kernel coding style](https://www.kernel.org/doc/html/latest/process/coding-style.html).
+
+
+* Stage your changes:
+
+        git add <file1> <file2> ...
+
+* Commit with a message.
+
+        git commit
+
+    The message should describe your changes. See [this link](https://docs.kernel.org/process/submitting-patches.html#describe-your-changes) for details.
+    Here is an example of commit message format:
+
+        Subsystem: Brief summary
+
+        More detailed explanation if needed, wrapped at 72 chars.
+
+    The `Subsystem` means: which part of the code your change touches.
+    For example, it could be "tcp", "test", and "doc" etc.
+
+    If there are some references, use "Links: " tag for anything.
+
+    Besides, passt uses the Linux kernel's "Signed-off-by" process. If you can
+    certify the below:
+
+        Developer's Certificate of Origin 1.1
+
+        By making a contribution to this project, I certify that:
+
+            (a) The contribution was created in whole or in part by me and I
+                have the right to submit it under the open source license
+                indicated in the file; or
+
+            (b) The contribution is based upon previous work that, to the best
+                of my knowledge, is covered under an appropriate open source
+                license and I have the right under that license to submit that
+                work with modifications, whether created in whole or in part
+                by me, under the same open source license (unless I am
+                permitted to submit under a different license), as indicated
+                in the file; or
+
+            (c) The contribution was provided directly to me by some other
+                person who certified (a), (b) or (c) and I have not modified
+                it.
+
+            (d) I understand and agree that this project and the contribution
+                are public and that a record of the contribution (including all
+                personal information I submit with it, including my sign-off) is
+                maintained indefinitely and may be redistributed consistent with
+                this project or the open source license(s) involved.
+
+    Add this line:
+
+	    Signed-off-by: Random J Developer <random@developer.example.org>
+
+    using your real name (sorry, no pseudonyms or anonymous
+    contributions.)  This will be done for you automatically if you use
+    `git commit -s`.  Reverts should also include "Signed-off-by". `git
+    revert -s` does that for you.
+
+    Any further SoBs (Signed-off-by:'s) following the author's SoB are
+    from people handling and transporting the patch, but were not involved
+    in its development. SoB chains should reflect the **real** route a
+    patch took as it was propagated to the maintainers, with the first SoB
+    entry signalling primary authorship of a single author.
+
+### 4. Generate Patches
+
+Use `git format-path` to generate patch(es):
+
+    git format-patch -o outgoing/ origin/master
+
+It will generate numbered patch files such as 0001-...patch, 0002-...patch 
+etc. in the `outgoing` folder.
+
+Or you can use `git format-patch -n`. For exmaple if you want to format just
+three patches:
+
+    git format-patch -3 -o outgoing/
+
+If you send a series of patches, use the `--cover-letter` option with
+`git format-patch`:
+
+    git format-patch -o outgoing/ origin/main --cover-letter
+
+This will generate a cover letter besides your patches. You can edit the cover
+letter before sending.
+
+### 5. Send Patches
+
+Use `git send-email` to send patches directly to the mailing list:
+
+    git send-email --to=passt-dev@passt.top 000*.patch -o outgoing/000*.patch
+
+If there are CCs (e.g. maintainers, reviewers), you can add them with `--cc`:
+
+    git send-email --to=passt-dev@passt.top --cc=maintainer@example.com 
+    outgoing/000*.patch
+
+### 6. Responding to Review Feedback
+
+* Be open to feedback on both code and documentation.
+
+* Update your patch as needed, and regenerate patches:
+
+        git add <file1> <file2> ...
+        git commit --amend
+        git format-patch -v2 origin/master
+
+* Send the revised patches
+
+        git send-email --to=passt-dev@passt.top v2-000*.patch
+
+### 7. Tips and Best Practices
+
+* Keep changes focused and easy to review. Please refer to [split-changes](https://docs.kernel.org/process/submitting-patches.html#split-changes)
+  to seperate each logical change into a separate patch.
+
+* Test your changes thoroughly. Refer to [test/README.md](/passt/tree/test/README.md)
+  for testing.
+  It's recommended to run at least a 'make cppcheck' and 'make clang-tidy'
+  other than a specific manual test of the functionality  / issue at hand.
+
+* Include documentation updates if your change affects usage.
+
+Thank you for helping improve passt! Your contributions make a big difference.
diff --git a/README.md b/README.md
index 8f188f4..6ba6441 100644
--- a/README.md
+++ b/README.md
@@ -553,7 +553,7 @@ See also the [test logs](/builds/latest/test/).
         man ./passt.1
 
 * run the demo script, that detaches user and network namespaces, configures the
-  new network namespace using `pasta`, starts `passt` and, optionally, `qemu`:
+  new network namespace using `pasta`, starts `passt` *and, optionally,* `qemu`:
 
         doc/demo.sh
 
@@ -625,7 +625,9 @@ See also the [test logs](/builds/latest/test/).
 
 ### [Mailing Lists](/passt/lists)
 * Submit, review patches, and discuss development ideas on
-  [`passt-dev`](https://lists.passt.top/postorius/lists/passt-dev.passt.top/)
+  [`passt-dev`](https://lists.passt.top/postorius/lists/passt-dev.passt.top/). 
+  Please refer to the [CONTRIBUTING.md](/passt/tree/CONTRIBUTING.md) for
+  details.
 
 * Ask your questions and discuss usage needs on
   [`passt-user`](https://lists.passt.top/postorius/lists/passt-user.passt.top/)
-- 
2.47.0