Enhance CONTRIBUTING.md with a Community Section

The repo could better guide new contributors by detailing where to ask questions, style checks, and feature roadmap.

## Details

We should:
- Add sections to `CONTRIBUTING.md`:
  - How to get help: discussions, etc.
  - PR template checklist.
  - Mentions of code style, commit message guidelines.
  - Link to roadmap or project board.

This helps orient newcomers and standardizes contributions.