docs: Added section describing Launcher Shortcuts.
docs: Added section describing Launcher Shortcuts.

The "Android N for Developers" page within the Android N preview
documentation now includes a section discussing the features and
workflow associated with Launcher Shortcuts.

Bug: 27753707
Change-Id: I43c17960f08a3c2a9e123ca5b5c411381afdfab8

xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base