Update bro-aux documentation

Added installation instructions and description of bro-cut.
Removed outdated material (discussion of localnetMAC.pl perl script, and
the reference to terminate_connection() in conn.bro).
Merge remote-tracking branch 'origin/topic/dnthayer/documentation'

* origin/topic/dnthayer/documentation:
  Update bro-aux documentation

BIT-1078 #merged