add RXD pin

README

@@ -4,6 +4,7 @@ We want port Openmoko to Pi, All free software
 1. open the case
 2. take off the cover of PCB
    then you will send the "GND" and "TXD"
+   and th TP74 is the "RXD"
    you can get serial output from those pins 
 
 3. you need a "RS-232 <--> TTL" converter to