Add docs for adding a new SDL server to the code

DEVELOPING.md

@@ -71,3 +71,10 @@ echo 'source $HOME/.cargo/env' >> $HOME/.bashrc
 ./win-static-build.sh
 
 ```
+
+# Adding a new SDL lite server backend to the code
+
+  * Add the new server name to the array in getRandomServer() in settings.cpp
+  * Add the new server to dropdown in mainwindow.cpp
+
+TODO: Make both of these places use a single list of servers.