Merge "Adding some Shell documentation" into tm-qpr-dev am: 5ff3c0e9 am: 8c573d92

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/19230676



Change-Id: I22661eb2608317d1bb74425b9d977764e4c45c1d
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>