Update adafruit_ble_radio.py

Fix missing timeout param documentation for receive. (present is receive_full but not receive).

Author: infamy

adafruit_ble_radio.py

@@ -146,6 +146,8 @@ def receive(self, timeout=1):
         """
         Returns a message received on the channel on which the radio is
         listening.
+        
+        :param float timeout: The length of time (in seconds) the radio listens for a broadcast
 
         :return: A string representation of the received message, or else None.
         """