Chromium OS-specific doc

This provides some information about Chromium OS and U-Boot.

• Chromium OS Support in U-Boot
  • Introduction
  • Talks and documents
• Running U-Boot with Chromium OS verified boot
  • Sandbox
  • Samus
  • Boot flow
  • New uclasses
  • Commands
  • Config options
  • Device-tree config
  • Porting to other hardware
  • Tests
  • U-Boot without Chromium OS verified boot
• Running U-Boot from coreboot on Chromebooks
  • Snow (Samsung ARM Chromebook)
  • Nyan-big
  • chromebook_jerry
  • Other notes