website: address several remaining TODOs

In particular:
- Reconciled install instructions
- Added favicons
- Made heading sizes consistent across pages
- Added content to a couple stubbed-out pages

Install instructions reconciled roughly as described here:
https://docs.google.com/document/d/1ysNCGvbSTVB06qA2zsomBc5rEu8xSGCntPUXLoLVPRI/edit

This isn't perfect, but given our current state it seems
reasonable, and should reduce confusion from external
developers. We can iterate further on the setup as we get
feedback.

Change-Id: I7420fcfe880302d716e848e55a776390bdcbd4eb
69 files changed