Merge "docs: Update READ_EXTERNAL_STORAGE explanation" into tm-dev am: 19a290e3

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/20066630



Change-Id: Iac1935168e91778afa50d1a07fd7e352c1a32fca
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>