Document ChangeLog policy change

Changelog

@@ -1,3 +1,13 @@
+For the latest changes please refer to the output of `git log` or the
+on-line log at:
+
+      https://alioth.debian.org/plugins/scmgit/cgi-bin/gitweb.cgi?p=sane/sane-frontends.git;a=log
+
+Note to developers:
+      For 1.0.15 and beyond we will generate the ChangeLog from the git
+      commit messages at release time.  Instead of documenting your work
+      here, just document it in your commit messages.
+
 2014-06-05 Tom Callaway <spot@fedoraproject.org>
 	* lib/snprintf.c: update to newer version from LPRng. The old version is
 	licensed under the Artistic License 1.0 which isn't compatible with the