Add USB to how_to_api.md

Amanda Butler · web-flow · commit f3e33f666c34 · 2019-02-28T14:54:25.000-06:00
Add USB audio player to list of API-based tutorials.
diff --git a/docs/tutorials/using_apis/how_to_api.md b/docs/tutorials/using_apis/how_to_api.md
@@ -16,6 +16,12 @@ ___
 
 ___
 
+
+### USB
+
+- [USB audio player](mbed-usb-wav-audio-player.html).
+
+___
 ### Drivers
 
 - [Flow control using Ticker and Wait](application-flow-control.html).
