Use a template to set the footer on ChangeEmails.

Add an admin editable ChangeFooter.vm template used to
format the footer in ChangeEmails.

Change-Id: I8f6f80b7a3e1fdb39ee1ea20aa84738286bce826
diff --git a/Documentation/config-mail.txt b/Documentation/config-mail.txt
index 3f891c9..5d38ed7 100644
--- a/Documentation/config-mail.txt
+++ b/Documentation/config-mail.txt
@@ -25,6 +25,12 @@
 one to set the subject line, and one to set the footer which gets appended to
 all the change emails (see `ChangeSubject.vm` and `ChangeFooter.vm` below.)
 
+ChangeFooter.vm
+~~~~~~~~~~~~~~~
+
+The `ChangeFooter.vm` template will determine the contents of the footer
+text that will be appended to emails related to changes (all `ChangeEmails)`.
+
 ChangeSubject.vm
 ~~~~~~~~~~~~~~~~