[openaddresses] adding Montana

resources/parser/data_sets/openaddresses.yaml

@@ -823,6 +823,12 @@ countries:
                       add_osm_boundaries: true
                     - filename: simpson.csv
 
+            mt:
+                add:
+                    state: MT
+                files:
+                    - filename: statewide.csv
+
             nc:
                 add:
                     state: NC