autojoin room config

homeserver.yaml.tmpl

@@ -1299,8 +1299,10 @@ account_threepid_delegates:
 # If the room already exists, make certain it is a publicly joinable
 # room. The join rule of the room must be set to 'public'.
 #
-#auto_join_rooms:
-#  - "#example:example.com"
+{{ if eq (env "AUTO_JOIN_ROOM_ENABLED") "1" }}
+auto_join_rooms:
+  - "{{ env "AUTO_JOIN_ROOM" }}"
+{{ end }}
 
 # Where auto_join_rooms are specified, setting this flag ensures that the
 # the rooms exist by creating them when the first user on the