Response to '$' help command also sends an 'ok'

Grbl-v1.1-Commands.md

@@ -28,6 +28,7 @@ Type $ and press enter to have Grbl print a help message. You should not see any
 
 ```
 [HLP:$$ $# $G $I $N $x=val $Nx=line $J=line $SLP $C $X $H ~ ! ? ctrl-x]
+ok
 ```
 
 The ‘$’-commands are Grbl system commands used to tweak the settings, view or change Grbl's states and running modes, and start a homing cycle. The last four **non**-'$' commands are realtime control commands that can be sent at anytime, no matter what Grbl is doing. These either immediately change Grbl's running behavior or immediately print a report of the important realtime data like current position (aka DRO). There are over a dozen more realtime control commands, but they are not user type-able. See realtime command section for details.