[outputs] Added documentation for forward imports

beat/core/outputs.py

@@ -30,7 +30,10 @@
 outputs
 =======
 
-Coming directly from beat.backend.python
+Forward imported from :py:mod:`beat.backend.python.outputs`:
+:py:class:`beat.backend.python.outputs.SynchronizationListener`
+:py:class:`beat.backend.python.outputs.Output`
+:py:class:`beat.backend.python.outputs.OutputList`
 """