Doc update

[zachcran]

This issue is migrated from CMakeDev issue 2, along with the migration of CMakeDev content into this repo.

"The developer documentation is likely to be quite stale (I believe most of it was written back when there was only a single repo). For this issue:

• Make sure terms (particularly CMakePP vs CMaize) are being used correctly
• Migrate the "other relveant projects" part to the relevant repos (I think mainly CMaize)
• Probably should add a section on how to unit test new CMake/CMakePP functions
• There should be some project-wide CI notes (like pointing out the .github and the .github.io repos)
  "

New bullets:

• There are warnings during documentation build that should be fixed.