Rewrite Patrole README to be high-level document

This commit improves the Patrole README by making it a high-level
introduction to Patrole. Implementation-specific details have been
removed from the README; they will be included in greater detail
in the Patrole documentation in a follow-up commit.

Change-Id: I6a0b4a4ef8017df24a8b8465750dae21039b1afc
Depends-On: I4d468b7f1bb6a000fde42d656635159176d5ef7f
1 file changed