Add master-tag file, identifies date of last pull

Add master-tag file, identifies date of last pull

Every time John Linville pulls in patches and pushes
them out he adds a tag. We now have this tag in the
master-tag file which should help identify the last
date of set of patchsets which compat-wireless is using.

This should help debugging issues with users.

Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>