Add section in README on how to contribute doc pages

[bourque]

The section should detail how to contribute new documentation pages, with link(s) to resources on how to write in ReStructured Text format.

[bourque]

We could also add some notes about common styles/formatting we are using, e.g. how we want to credit original authors.

[bourque]

Also mention something about language and tone, e.g. avoid opinions without supporting facts, avoid using first-person, opinions get put under "Lessons Learned" section, etc.

[bourque]

• Point to guideline template
• Using discussions
• Point to Markdown help
• Where to place docs within organization
• How to set up virtual environment (IMAP has poetry docs already) (Provide a requirements.txt file)
• Describe the scope (not meeting notes, information useful to DS that grows, ecosystem for in-depth technical knowledge)
• Make it clear that this is a public repo/documentation (no credentials, CUI, etc.) (this can go under scope section)