🚑 add gitter_room badge, fix #32

Author: jayvdb

templates/badges.rst.jj2

@@ -14,5 +14,7 @@
    :target: https://codecov.io/gitlab/{{organisation}}/{{name}}
 {% endif %}
 
+{% if gitter_room %}
 .. image:: https://img.shields.io/gitter/room/gitterHQ/gitter.svg
-   :target: https://gitter.im/pyexcel/Lobby
+   :target: https://gitter.im/{{gitter_room}}
+{% endif %}