Add pointer to where the GFDL can be found.

man/erc.texi

@@ -20,7 +20,14 @@ Copyright @copyright{} 2005, 2006, 2007 Free Software Foundation, Inc.
 Permission is granted to copy, distribute and/or modify this document
 under the terms of the GNU Free Documentation License, Version 1.2 or
 any later version published by the Free Software Foundation; with no
-Invariant Sections, Front-Cover texts, or Back-Cover Texts.
+Invariant Sections, Front-Cover texts, or Back-Cover Texts.  A copy of
+the license is included in the section entitled ``GNU Free
+Documentation License'' in the Emacs manual.
+
+This document is part of a collection distributed under the GNU Free
+Documentation License.  If you want to distribute this document
+separately from the collection, you can do so by adding a copy of the
+license to the document, as described in section 6 of the license.
 
 All Emacs Lisp code contained in this document may be used, distributed,
 and modified without restriction.