quad: Add instructions for using PWM signals on the virtual quad

quad/src/virt_quad/README.md

@@ -14,4 +14,11 @@ make run
 ```
 
 And you can do things with it. You'll notice it will make a bunch of FIFOs in
-the current directory. Write to / read from these FIFOs as you see fit.
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+the current directory. Write to / read from these FIFOs as you see fit.
+
+## Writing to FIFO from shell
+
+```
+echo "170000" > virt-quad-fifos/pwm-input-gear  # Setting the gear to '1'
+cat virt-quad-fifos/pwm-output-motor1           # Read the motor 1 pwm signal
+```
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