Authors: make it more clear what refers to borg and what to attic

With some sphinx output formats (e.g. "man") that was not too
clear before this change.

AUTHORS

@@ -1,23 +1,24 @@
-Contributors ("The Borg Collective")
-====================================
+Borg Contributors ("The Borg Collective")
+=========================================
 
 - Thomas Waldmann <tw@waldmann-edv.de>
 - Antoine Beaupré <anarcat@debian.org>
 - Radek Podgorny <radek@podgorny.cz>
 - Yuri D'Elia
 
+Borg is a fork of Attic.
+
 Attic authors
 -------------
 
-Borg is a fork of Attic. Attic is written and maintained
-by Jonas Borgström and various contributors:
+Attic is written and maintained by Jonas Borgström and various contributors:
 
-Development Lead
-````````````````
+Attic Development Lead
+``````````````````````
 - Jonas Borgström <jonas@borgstrom.se>
 
-Patches and Suggestions
-```````````````````````
+Attic Patches and Suggestions
+`````````````````````````````
 - Brian Johnson
 - Cyril Roussillon
 - Dan Christensen