Add comments and explanation to joint_diagnostic

src/picknik_ur_mock_hw_config/objectives/joint_diagnostic.xml

@@ -1,11 +1,13 @@
 <?xml version='1.0' encoding='UTF-8'?>
 <root BTCPP_format="4" main_tree_to_execute="Joint Diagnostic">
   <!-- ////////// -->
-  <BehaviorTree ID="Joint Diagnostic" _description="Move to a known pose and cycle through the min and max limits of a joint repeatedly" _favorite="true">
+  <BehaviorTree ID="Joint Diagnostic" _description="Example of cycling through the min and max limits of a single joint, for hardware testing" _favorite="true">
     <Control ID="Sequence" name="TopLevelSequence">
+      <!--Setup by moving home-->
       <SubTree ID="Move to Waypoint" waypoint_name="Home" joint_group_name="manipulator" controller_names="/joint_trajectory_controller /robotiq_gripper_controller" planner_interface="moveit_default"/>
       <Decorator ID="KeepRunningUntilFailure">
         <Control ID="Sequence">
+          <!-- If you use two waypoints that have identical joint values, except for one joint, you can use this Objective as a way to test a single joint repeatedly. This is useful for things like hardware diagnostics and hardware bringup.-->
           <SubTree ID="Move to Waypoint" waypoint_name="Wrist 2 Max" joint_group_name="manipulator" controller_names="/joint_trajectory_controller /robotiq_gripper_controller" planner_interface="moveit_default"/>
           <SubTree ID="Move to Waypoint" waypoint_name="Wrist 2 Min" joint_group_name="manipulator" controller_names="/joint_trajectory_controller /robotiq_gripper_controller" planner_interface="moveit_default"/>
         </Control>