note aout cordio port

Author: paul-szczepanek-arm

BLE_SM/README.md

@@ -25,3 +25,5 @@ Hardware requirements are in the [main readme](https://github.com/ARMmbed/mbed-o
 ## Building instructions
 
 Building instructions for all samples are in the [main readme](https://github.com/ARMmbed/mbed-os-example-ble/blob/master/README.md).
+
+Note: example currently doesn't use ST provided stack and instead uses a Cordio port for the ST.