Update intro_to_nav.md

ros1/intro_to_nav.md

@@ -18,6 +18,10 @@ Visualize the simulated robot in Rviz:
 roslaunch stretch_gazebo gazebo.launch rviz:=true
 ```
 
+## Untethered Operation
+
+At this point, we want to remove all wires tethered Stretch to our monitor/keyboard/etc. We'll set up "ROS Remote Master", which is a feature built into ROS that allows untethered operation. Follow this guide: https://docs.hello-robot.com/0.2/stretch-tutorials/getting_started/untethered_operation/#ros-remote-master
+
 ## Teleoperation
 
 Switch to 'navigation' [mode](https://github.com/hello-robot/stretch_ros/tree/noetic/stretch_core#mode-std_msgsstring):
@@ -69,4 +73,10 @@ angular:
 ---
 ```
 
+### Safety
+
+Velocity commands must be sent at a regular control rate and must be faster than 2hz. There's two safety behaviors that prevent a runaway robot. A software check smoothly stops base motion after 0.5 seconds if no new command is received. A hardware check abruptly stops base motion after 1 second if no new command is received.
+
 ## Mapping
+
+TODO