Add contact charger usage

docs/getting_started/basic_usage.rst

@@ -44,5 +44,27 @@ The SLATE base comes with a plug-in battery charger with the following specifica
 * 5A
 * 160W
 
-To charge the SLATE base's battery, plug the charger's barrel jack into the base's Charger Port.
+To charge the SLATE base's battery with the plug-in charger, plug the charger's barrel jack into the base's Charger Port.
 See the :ref:`getting_started/basic_usage:Rear Interface Panel` for details on the port.
+
+While charging, the plug-in charger's LED will be red.
+When fully charged or disconnected, the plug-in charger's LED will be green.
+
+Contact Charger
+===============
+
+The SLATE base comes with a contact charger.
+
+To charge the SLATE base's battery with the contact charger, follow the procedure below:
+
+#.  Plug the plug-in charger into the contact charger's barrel jack port.
+#.  Press the power button on the contact charger to turn it on.
+    The power button will turn green when on.
+#.  Drive the SLATE base into the contact charger, ensuring that both pads on the base and the retractable contacts on the contact charger are touching.
+#.  Use the ``enable_charging`` service of the SLATE's ROS driver to activate the base's internal charging relay.
+#.  Check the following two indications to ensure the base is charging:
+
+    * The light on the top of the contact charger turns green
+    * The base's screen reports a "Charging" status
+
+#.  The light on the top of the contact charger will turn off when the base is fully charged.