Add note about Tiled version

README.md

@@ -83,6 +83,9 @@ curl \
   https://matrix.org/_matrix/client/r0/rooms/%21roomid%3Amatrix.org/state/team.auglement.augmentile.map/mymap
 ```
 
+You need at least Tiled version 1.6 for this to work due to an
+[incompatible type used before](https://github.com/mapeditor/tiled/issues/3033).
+
 #### Personal maps
 
 Each user in a room can add a personal map under their personal state key. To do this,