docs: Add dependency and version change guidelines (#3745)

* Add dependency and version change guidelines

Added guidelines for managing dependencies and version changes to ensure stability in the Awkward ecosystem.

* Format contributing guidelines for clarity

Author: ianna

CONTRIBUTING.md

@@ -314,3 +314,41 @@ python -m pip install --upgrade awkward
 python -m pip uninstall --yes awkward awkward-cpp
 python -m pip install --upgrade --extra-index-url https://pypi.anaconda.org/scientific-python-nightly-wheels/simple awkward
 ```
+
+### Guidelines for Dependency and Version Changes
+
+To ensure stability and reproducibility across the Awkward ecosystem:
+
+1. Collaborative Review Required
+   - Pull requests that affect core dependencies (e.g., Numba, Pandas, PyArrow, NumPy) or Python version support must be discussed with maintainers before merging.
+   - This avoids unilateral decisions that could break critical workflows.
+
+2. Compatibility Transparency
+   - If a dependency is not yet available for a new Python release, note this clearly in the PR description and documentation.
+   - Example: “Supports Python 3.14, but Numba-dependent features are disabled until upstream support is released.”
+
+3. Testing Expectations
+   - CI should run against all supported Python versions.
+   - Tests that depend on unsupported features (e.g., Numba on Python 3.14) must be marked with xfail so contributors see the limitation.
+
+4. Version Pinning
+   - Pin or constrain versions of critical dependencies to prevent silent breakages from upstream changes.
+   - Floating versions may be allowed for secondary utilities, but core scientific packages should be locked.
+
+5. Communication
+   - Use GitHub Discussions or Issues to propose changes before opening a PR that alters compatibility.
+   - This ensures consensus and avoids surprises for downstream users.
+
+
+
+---
+
+#### Example PR Checklist
+
+- Have I discussed this change with maintainers?
+
+- Did I document limitations (e.g., missing Numba support)?
+
+- Are CI tests updated to reflect compatibility status?
+
+- Did I pin or constrain critical dependencies?