chore(kb): add article about controbuting.md

knowledge base/contributingmd.md

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+# CONTRIBUTING.md
+
+`CONTRIBUTING.md` files should be put in one's repository or website.<br/>
+It provides potential project contributors with a short guide to how they can help with the project.
+
+## TL;DR
+
+It is convention to:
+
+- Name the file `CONTRIBUTING.md` (all uppercase).
+- Put the file in the project's root directory.
+
+## Further readings
+
+### Sources
+
+- [How to Build a CONTRIBUTING.md]
+
+<!--
+  Reference
+  ═╬═Time══
+  -->
+
+<!-- In-article sections -->
+<!-- Knowledge base -->
+<!-- Files -->
+<!-- Upstream -->
+<!-- Others -->
+[How to Build a CONTRIBUTING.md]: https://mozillascience.github.io/working-open-workshop/contributing/