debian/changelog: document commenting out of all lines in debian/watch file

debian/changelog

@@ -59,6 +59,9 @@ mumble (1.3.0~git20190114.9fcc588+dfsg-1) UNRELEASED; urgency=medium
   * debian/upstream:
     - Remove signing-key.asc due to having to repack upstream tarball
       which will cause the PGP signature check to fail
+  * debian/watch:
+    - Comment out all lines for now, as the source of the tarball is
+      via git export of 'master' with submodules via a script
 
  -- Christopher Knadle <Chris.Knadle@coredump.us>  Mon, 14 Jan 2019 14:37:42 +0000