netman: update module description (#21664)

Co-authored-by: David Sidrane <David.Sidrane@Nscdg.com>
Co-authored-by: Hamish Willee <hamishwillee@gmail.com>

src/systemcmds/netman/netman.cpp

@@ -405,12 +405,24 @@ static void usage(const char *reason)
   memory. On boot the `update` option will be run. If a network configuration
   does not exist. The default setting will be saved in non-volatile and the
   system rebooted.
-  On Subsequent boots, the `update` option will check for the existence of
-  `net.cfg` in the root of the SD Card.  It will saves the network settings
-  from `net.cfg` in non-volatile memory, delete the file and reboot the system.
-
-  The `save` option will `net.cfg` on the SD Card. Use this to edit the settings.
-  The  `show` option will display the network settings  to the console.
+  
+  #### update
+  
+  `netman update` is run automatically by [a startup script](../concept/system_startup.md#system-startup).
+  When run, the `update` option will check for the existence of `net.cfg` in the root of the SD Card.
+  It then saves the network settings from `net.cfg` in non-volatile memory, 
+  deletes the file and reboots the system.
+
+  #### save
+  
+  The `save` option will save settings from non-volatile memory to a file named
+  `net.cfg` on the SD Card filesystem for editing. Use this to edit the settings. 
+  Save does not immediately apply the network settings; the user must reboot the flight stack.
+  By contrast, the `update` command is run by the start-up script, commits the settings to non-volatile memory, and reboots the flight controller (which will then use the new settings).
+  
+  #### show
+  
+  The `show` option will display the network settings in `net.cfg` to the console.
 
   ### Examples
   $ netman save           # Save the parameters to the SD card.