Support the inseretion of the public key from pem
files into the mac_permissions.xml file at build
time.

Change-Id: Ia42b6cba39bf93723ed3fb85236eb8f80a08962a

This README intends to document the various configuration options
that exist for specifiying device specific additions to the policy.

Change-Id: I7db708429a67deeb89b0c155a116606dcbbbc975