More details on adding a WA map to an assembly.

I added details on how an assembly can add an WA map room.

docs/maps.en.md

@@ -74,10 +74,12 @@ obvious violations (e.g. exits to nonexistant maps), or suggest improvements.
 To contribute maps to the world, you have to
 [register an assembly](https://maschinenraum.rc3.world/).
 
-Please store your maps in a git repo of your choice and and enter a (publicly
-clonable) URL to it our backend. Our infrastructure will then periodically pull
-your map in, run a rudimentary linter on it to check for a few requirements and
-general consistency, and then deploy it to rc3.world.
+Please store your maps in a git repo of your choice. Then add a new room to your 
+assembly. Click the button "create" in the "2D map" field. In the next window you can enter the (publicly clonable) URL of the git repo.  
+
+Our infrastructure will then periodically pull your map in, run a rudimentary 
+linter on it to check for a few requirements and general consistency, and then 
+deploy it to rc3.world.
 
 Please note that your map may also be rejected in case it contains errors (e.g.
 exits pointing to maps that do not exist) or is simply in the wrong format. If