add CONTRIBUTING guide

Author: mxpv

CONTRIBUTING.md

@@ -0,0 +1,37 @@
+# Contributing
+
+Pull requests are welcome!
+
+## Before Opening a PR
+
+Please ensure the following checks pass:
+
+1. Tests are passing:
+   ```bash
+   bazelisk test //...
+   ```
+
+2. Formatting is correct:
+   ```bash
+   bazelisk run :fmt
+   ```
+
+3. Lints are passing:
+   ```bash
+   bazelisk run :lint
+   ```
+
+## Documentation
+
+If new APIs are introduced, they must be documented.
+
+If documentation changes, regenerate the docs in a separate commit:
+```bash
+bazelisk run //docs:update
+```
+
+## PR Guidelines
+
+PR title will be included in the changelog, so make sure it clearly communicates the change.
+
+PR body should communicate the intent of the change - what it does and why.