am 618ded26: am a6602f1f: Add docs for SDK update. Add redirects for preview files. Manually integrate a few doc changes from cupcake.

Merge commit '618ded26c61afbf907e72b4568a4f4f1c6c287a7' into eclair-plus-aosp

* commit '618ded26c61afbf907e72b4568a4f4f1c6c287a7':
  Add docs for SDK update.