Add docstring for init request manager

src/primaite/simulator/system/applications/database_client.py

@@ -37,6 +37,11 @@ class DatabaseClient(Application):
         super().__init__(**kwargs)
 
     def _init_request_manager(self) -> RequestManager:
+        """
+        Initialise the request manager.
+
+        More information in user guide and docstring for SimComponent._init_request_manager.
+        """
         rm = super()._init_request_manager()
         rm.add_request("execute", RequestType(func=lambda request, context: RequestResponse.from_bool(self.execute())))
         return rm