Improve documentation of RSSI

Fixes #272

Author: elgohr

gap.go

@@ -106,7 +106,7 @@ type ScanResult struct {
 	// Bluetooth address of the scanned device.
 	Address Address
 
-	// RSSI the last time a packet from this device has been received.
+	// Signal strength of the  advertisement packet.
 	RSSI int16
 
 	// The data obtained from the advertisement data, which may contain many