Android S Beta 1
Adds a README and canonical example for treble_manifest_split.

Also updates the default ninja path to a valid path.

Bug: 186258929
Test: Follow the steps provided in the README to create a split
      manifest for aosp_arm64.
Change-Id: Ia5f7f2937f8b3d813678eea388bd16ec4a12e32f
3 files changed