add contributions policy CONTRIBUTING.md at the repo root

Signed-off-by: tdruez <tdruez@aboutcode.org>

Author: tdruez

CONTRIBUTING.md

@@ -0,0 +1,45 @@
+# Contributing to ScanCode.io
+
+Thank you for your interest in contributing to AboutCode projects.
+Please **read the following guidelines carefully before submitting a pull request**.
+
+## Pull request rules
+
+- **Attach your PR to an existing issue.** Discuss the approach and implementation
+  details in the issue first, before writing any code. Please note that if the issue
+  has already been assigned to someone else, you are welcome to comment on it, but it
+  would be best to contribute code in such a case only if you are invited to do so.
+
+- **You must fully understand your code changes** and be able to explain them
+  clearly. If you cannot walk a reviewer through your changes, the PR will not
+  be accepted.
+
+- **Write your own descriptions, comments, and documentation.** All written
+  content in a PR must be authored by a human.
+
+- **Disclose any AI usage.** If any part of your contribution was generated or
+  assisted by AI, you must disclose this and specify the tools used.
+
+- **Include tests.** Any code change or addition must be accompanied by proper
+  unit tests. Untested code will not be merged.
+
+**Any PR that violates these rules will be closed.**
+
+## Pull request tips
+
+To maximize your chances of a successful contribution:
+
+- **Keep changes focused.** Address only what the issue requires. Do not bundle
+  unrelated changes together.
+
+- **Be patient.** Do not solicit maintainers for a review.
+
+- **Remember:** project maintainers have no interest in reviewing code
+  generated by machines.
+
+- **Do not make structural changes** to the codebase such as adding type hints.
+
+## Ways to Contribute
+
+See https://scancodeio.readthedocs.io/en/latest/contributing.html for more ways to 
+contribute.

README.rst

@@ -27,8 +27,14 @@ The ScanCode.io documentation also provides:
 If you have questions that are not covered by our documentation, 
 please ask them in `Discussions <https://github.com/aboutcode-org/scancode.io/discussions>`_.
 
+Contributing
+============
+
+Thank you for your interest in contributing to AboutCode projects.
+Please `read the following guidelines carefully <https://github.com/aboutcode-org/scancode.io/blob/main/CONTRIBUTING.md>`_  before getting started.
+
 Build and tests status
-----------------------
+======================
 
 +------------+-------------------+
 | **Tests**  | **Documentation** |
@@ -37,7 +43,7 @@ Build and tests status
 +------------+-------------------+
 
 License
--------
+=======
 
 SPDX-License-Identifier: Apache-2.0
 
@@ -58,7 +64,6 @@ ScanCode.io should be considered or used as legal advice. Consult an Attorney
 for any legal advice.
 
 
-
 .. |ci-tests| image:: https://github.com/aboutcode-org/scancode.io/actions/workflows/run-unit-tests.yml/badge.svg?branch=main
     :target: https://github.com/aboutcode-org/scancode.io/actions/workflows/run-unit-tests.yml
     :alt: CI Tests Status
@@ -69,7 +74,7 @@ for any legal advice.
 
 
 Acknowledgements, Funding, Support and Sponsoring
---------------------------------------------------------
+=================================================
 
 This project is funded, supported and sponsored by: