LP#2051946: Add Co-authored-by to commit-template

Add an example for Co-authored-by entries to the commit-template.
This was requested by Mike Rylander in comment #3 of bug 2051946, and
seconded by Stephanie Leary.

Signed-off-by: Jason Stephenson <jason@sigio.com>

Author: Dyrcona

commit-template

@@ -12,6 +12,11 @@
 # Larger changes with extensive release notes in a separate file
 # and/or documentation updates may ignore the above.
 
+# Additional authors or direct contributors for a commit can be
+#  credited with lines like the followiing:
+## Co-authored-by: <Their Name <address@hostname.tld> >
+
+
 ## Signed-off-by: <Your Name <address@hostname.tld> >
 # Above can be done with -s option to git commit.