docs: add CONTRIBUTING.md with developer onboarding quickstart

Salim Zidanerequested to merge
gitlab-community/gitlab-org/orbit/knowledge-graph:824/add-contributing-md into main

What does this MR do and why?

Adds CONTRIBUTING.md at the root : an onboarding entry point for new and community contributors covering quickstart, testing, linting, and MR conventions.

Updates README.md to link to it.

Related Issues

Closes #824 (closed)

Testing

mise lint:docs passes.

Performance Analysis

  • This merge request does not introduce any performance regression. If a performance regression is expected, explain why.
Edited by Dmitry Gruzd (OOO from 2026-08-14 to 2026-08-27)

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