Add notes regarding public tags

docs/koji/addnewtag.md

@@ -32,3 +32,7 @@ In addition, please update the clone of this repo on lxsoftadm01:
 ```
 
 There should not be any locally-modified or untracked files on lxsoftadm01.
+
+# Public tags
+
+By default, tags will create repos under https://linuxsoft.cern.ch/internal/repos/. If the user requested a public tag/repo, it should be added to https://gitlab.cern.ch/linuxsupport/cronjobs/mash/-/blob/master/prod.config.yaml as well, so it can appear under <https://linuxsoft.cern.ch/repos/>.