Wrote some setup documenation about the new websocket feature.

SETUP.md

@@ -104,7 +104,8 @@ in the background. To start `mtwebmapper` use:
       -map=/path/to/your/map           \
       -web=/path/to/your/static/web    \
       -redis-host=localhost            \
-      -workers=2
+      -workers=2                       \
+      -websockets=false
 
 For the `colors=` options applys the same as said above. You can also add
 `-transparent=true` for transparency as mentioned above. The `web-host=` is the interface the
@@ -125,6 +126,19 @@ give to much ressources to this if you planning to run the mapping webserver on
 same machine as the Minetest server. On the other hand assigning more cores to it definitely
 helps to boost up the performance.
 
+Setting the`-websockets=true` flag enables websocket support for the server. With this
+feature turned on and changing the line (in `web/index.html`) from
+
+    var useWebsocket = false; // Set to true if you want websocket support
+
+to
+
+    var useWebsocket = true; // Set to true if you want websocket support
+
+the web client gets an extra 'auto update' mode. When switched on the server
+informs the client if something in the maps has changed. The displayed map will
+then update automatically. Of cause your browser needs Websocket support, too.
+
 ## Configure and restart the Minetest server
 
 Now everything is in place and the only thing left ist to re-configure the Minetest server