Split the sound effects examples.

Author: microbit-matt-hillsdon

src/demo.html

@@ -92,7 +92,8 @@ <h1>MicroPython-micro:bit simulator example embedding</h1>
               <option value="pin_logo">Pin logo</option>
               <option value="radio">Radio</option>
               <option value="sensors">Sensors</option>
-              <option value="sound_effects">Sound effects</option>
+              <option value="sound_effects_builtin">Sound effects (builtin)</option>
+              <option value="sound_effects_user">Sound effects (user)</option>
               <option value="speech">Speech</option>
               <option value="volume">Volume</option>
             </select>