Enable markdown in this warning box

Author: PeterJCLaw

programming/sr/motors/index.md

@@ -29,7 +29,7 @@ you could do this instead:
 R.motor_boards["srABC1"].something...
 ~~~~~
 
-<div class="warning">
+<div class="warning" markdown="1">
     When you have more than one Motor board connected to your kit,
     you must use `R.motor_boards` and index by serial number. This is so
     that the kit knows which Motor Board you want to control.