README add information missing from --scan-serial
diff --git a/README b/README
index f387d96..871382d 100644
--- a/README
+++ b/README
@@ -202,6 +202,16 @@ FPGA mining boards(BitForce, Icarus) only options:
--scan-serial|-S <arg> Serial port to probe for FPGA mining device
+ With "-S auto", BitForce enabled and only on linux, cgminer will attempt
+ to automatically find BitForce FPGA devices
+ Note that the computer may take some time to recognise the USB device
+ when it is first plugged in - especially if the system is slow or busy
+ (e.g. already GPU mining)
+
+ On linux <arg> is usually of the format /dev/ttyUSBn
+ On windows <arg> is usually of the format COMn
+ (where n = the correct device number for the FPGA device)
+
CPU only options: