Add custom test support documentation back

Author: virtuald

docs/custom.rst

@@ -4,4 +4,16 @@
 Custom Test Support
 ===================
 
-Test support has not yet been upgraded for 2020.
+.. contents::
+
+pytest fixtures
+---------------
+
+.. automodule:: pyfrc.test_support.pytest_plugin
+   :members:
+
+Controlling the robot's state
+-----------------------------
+
+.. automodule:: pyfrc.test_support.controller
+   :members:

pyfrc/test_support/controller.py

@@ -8,6 +8,10 @@
 
 
 class TestController:
+    """
+    Use this object to control the robot's state during tests
+    """
+
     def __init__(self, reraise, robot: wpilib.RobotBase):
         self._reraise = reraise