docs: Add video to Instant Apps landing page
docs: Add video to Instant Apps landing page

b/28842359

Change-Id: Idb097501425ca0a50f547a22f54217878075376a

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