Adds docstring to System class, makes system.rst

docs/reference/index.rst

@@ -29,4 +29,5 @@ decisions are made, see the :doc:`/discussion/index` section.
    camera
    directions
    deprecations
+   system
    features/index

docs/reference/system.rst

@@ -0,0 +1,11 @@
+.. py:currentmodule:: ppb.systemslib
+
+================
+System
+================
+
+.. automodule:: ppb.systemslib
+
+.. autoclass:: ppb.systemslib.System
+    :members:
+

ppb/systemslib.py

@@ -1,13 +1,18 @@
 """
-Systemslib is the core class for new subsystems. Systems add new features to 
+:class:`~ppb.systems.systemlib.System` is the core class for new subsystems. Systems add new features to 
 the core ppb engine.
 """
 
 import ppb.gomlib
 
-
 class System(ppb.gomlib.GameObject):
+    """ 
+    Creates an object capable of modifying the engine itself. 
 
+    All systems are context managers. For more see `Python context manager docs <https://docs.python.org/3/library/stdtypes.html#typecontextmanager>`_
+    Set-up and teardown with __enter__ and __exit__ methods.
+    Subclass examples include :class:`~ppb.systems.renderer.Renderer` `~ppb.systems.clocks.Updater`
+    """
     def __enter__(self):
         pass