Add more info to Docs README

[lzdanski]

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After making a couple of my own docs PR's and helping some colleagues work with Sphinx, wanted to add some more detailed information to the Docs Readme that have commonly come up.

• Adds link to Docs Readme from main Contributing Guide.
• Copyediting of existing Readme content.
• Adds information about the workflow for making docs changes, recommendations about where to edit for particular kinds of docs changes (local vs in GitHub), and explains how to use local builds for QC testing.
• Describes where and how to find the source content for updating docs, since some content is autogenerated from strings in Python files.
• Add information about the Docs CI/CD tests that must pass before merging and how to run them locally before submitting a PR.
• Adds a troubleshooting section to the readme that documents the common error UNEXPECTED UNINDENT and resolution as well as the existing Sphinx bug that reports the incorrect line number.

Other considerations:

• Is there a standard number of characters in each line we'd like Docs to use or when to include line breaks? It looks like we all use somewhat different line lengths.

[potiuk]

In the new version of build-docs (since ~ 3 months) you can simply specify package names as arguments without --package-filter - they are also autocomplete'able.

[potiuk]

You can add empty __init__.py and pre-commit should add the licence automatically as well.

[potiuk]

Very nice! Thanks. There are a few NITs, and clarifications but it's great to see more guidelines for the contributors.

[josh-fell]

This is tremendous! Only one question/suggestion.

[potiuk]

static checks :)

[josh-fell]

🚀