Add CONTRIBUTING.md pointing to README

[KonstantinMB]

The README has a full Contributing section, but GitHub also looks for a CONTRIBUTING.md at the repo root — it surfaces the file in the PR creation UI and on the Issues page ("contributing guidelines" link). Right now neither shows up.

What to do

• Create CONTRIBUTING.md at the repo root
• Keep it short — a 4–6 bullet TL;DR — and link out to the Contributing section of the README for the detail
• Mention the issue templates and the idea label
• Note that PRs need 1 approval and that admin (the maintainer) bypasses that on their own merges

Acceptance criteria

• CONTRIBUTING.md exists at repo root
• Has a "Quick start for contributors" section pointing to README
• Mentions: open an issue first for non-trivial work, branch naming (feature/x or fix/x), one-feature-per-PR rule
• The "Contributing" link in the GitHub Issues UI resolves to this file

Scope

Touches 1 file. Estimated time: 15-30 minutes.

Want to take this on? Comment below and I'll assign it to you.