am a9b9e3f7: am 930189f0: am df71cabb: cherrypick Change-Id: Ica1b68a1687917432d39d7d116c9c24fa1644a83 Initial posting of in-app billing docs

* commit 'a9b9e3f7a955888c44ecfba6cf29c420862976d2':
  cherrypick Change-Id: Ica1b68a1687917432d39d7d116c9c24fa1644a83 Initial posting of in-app billing docs