CB-5122 Document workflows

First pass on CB-5122, trying to clarify the two different Workflows ("Web Project Dev vs Native Project Dev").

Still have things to add to this pull request but I wanted to put something up to start getting some reviews.

Next:
- Go through each of the "{Platform} Command-line Tools" pages and verify that each page 1) mentions the different workflows and which workflow said page is a part of, 2) lists all available command lines tools, 3) links to Plugman guide
- Expose "Using Plugman" guide as a top level guide, it should be accessible on the left hand menu
- Update "Using Plugman" guide, move most of the Plugman's README.md content into this guide