Update OSM tag mapping docs

Author: vesameskanen

doc/user/osm/Default.md renamed to doc/user/osm/OsmTag.md

@@ -74,7 +74,7 @@ nav:
     - Introduction: 'Configuration.md'
     - Build: 'BuildConfiguration.md'
     - OSM Tag Mapping:
-        - Default: 'osm/Default.md'
+        - Default: 'osm/OsmTag.md'
         - Finland: 'osm/Finland.md'
         - Germany: 'osm/Germany.md'
         - Norway: 'osm/Norway.md'