Add copyright blurb for https://github.com/RichiH/vcsh/issues/121

tools/list_CONTRIBUTORS

 #!/bin/sh
 
+# This program is licensed under the GNU GPL version 2 or later.
+# (c) Richard "RichiH" Hartmann <richih@debian.org>, 2012-2014
+# For details, see LICENSE. To submit patches, you have to agree to
+# license your code under the GNU GPL version 2 or later.
+
+
 echo 'Alphabetical list of surnames of everyone who ever committed to this repository.
 Auto-generated from tools/list_CONTRIBUTORS.
 '