Android aosp: refactor roll_aosp.sh, add docs A few minor simplifications and documenting some caveats. Bug: b/279980674 Change-Id: I895721a97f9aa849a2cd6a67fe3a76098c10e9e9 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5845911 Reviewed-by: Yuxin Hu <yuxinhu@google.com> Reviewed-by: Cody Northrop <cnorthrop@google.com>