Update maps.md --> `"copyright"` Property fixed, minor spelling

docs/maps.en.md

@@ -149,6 +149,8 @@ Tiles can also be transparent, and are saved in the PNG format.
 * Check the license of the tiles!
     * We will not actively check the licenses of your tiles, but react to 
       violations on a "takedown on notice" principle!
+    * Document the license of your tiles via the custom property
+      `tilesetCopyright` (type string) on the tileset.
 * [Shared Tiles Repo](https://tiles.rc3.world/)
 
 ### How to design / "pixel" tiles
@@ -212,6 +214,10 @@ in the TSX format is not possible. (This does not mean that the image data itsel
 will be embedded. PNG must be included in the repository as seperate files as
 well.)
 
+Please pay attention to the licenses of the tiles you use, and document their
+copyright by setting the `tilesetCopyright` custom property (type string) on each
+tileset.
+
 ### Additional functionality per layer
 
 #### Start layer
@@ -351,8 +357,8 @@ To do so just untick the "infinite" tick box, then save.
 
 ## Licenses
 Please pay attention to the licenses and copyright of your tilesets. You must (!)
-set those via the `copyright` property directly on the tilesets within your map
-json! (just add a custom property to the tileset in Tiled).
+set those via the `tilesetCopyright` property directly on the tilesets within 
+your map json! (just add a custom property to the tileset in Tiled).
 
 The same applies to your entire map: document its licence / copyright by setting
 the property `mapCopyright` (type string) on the map (not on a layer / tileset!).