Doc: Ways to contribute

This issue will need some more discussion before it is ready for writing. This is what I would like for this to cover - we will nail down details

- Finding a task
- `good first issue` and `needs help` tags in issues
- Participate in discussions - either propose a new analysis or changes an existing one, help shape the design of a proposed analysis
- Fix a bug (probably not relevant when we launch)

Another thing that would be nice to have is to match up skills with the analyses with will be starting with like:
- If you have expertise in cell identification (example), you can contribute to Y analysis

This idea is based on [Firefox contributing docs](https://firefox-source-docs.mozilla.org/contributing/contributing_to_mozilla.html)

Start by reviewing the proposed scope in issue #147 and the linked Firefox contributing documentation. Discuss and settle the contribution paths and skills-to-analysis matching before writing. Done means the agreed contribution guidance is documented and covers the listed ways to participate.

Written by the indexing model from the issue text.