Draft a "How to Contribute" page

[larrybabb]

We have had several requests for contributions and we are an open-source project, so we should have a "How to contribute" page in our repo which is called out on the Readme.md.

Ideally someone can pick this up and draft an outline with some suggested process so we can begin refining and publishing it.

[korikuzma]

• Squash and merge
• Conventional Commits
  • Use conventional commits for PRs

[korikuzma]

Example of contributing docs from biocommons.hgvs: https://hgvs.readthedocs.io/en/stable/contributing.html