Reorganize and update documentation

[ironnysh]

What is this PR doing?

1. Reorganizing the Contributing chapter of the docs, and updating the content. See this issue

2. Adding references to the Developer docs in relevant Blueprints steps. See Improve the description of SetSiteOptionsStep #1291.

### To-Do:

• Update wp-now README.

Done in Update wp-now documentation #251.

Testing Instructions

1. Build the site (standard npm run build to update the steps in packages/playground/blueprints/src/lib/steps/)
2. Run npm run dev:docs.
3. Review the changes.

@adamziel

[adamziel]

Pure awesomeness @ironnysh, thank you so much for this! I only left one substantial note and it looks great otherwise. Feel free to merge once it's adjusted!