readme: debug instructions and screen instructions

README.md

@@ -21,6 +21,21 @@ zig build
 zig build qemu
 ```
 
+#### Debugging with GDB
+
+```
+zig build qemu -Dgdb
+```
+
+In another terminal:
+
+```
+gdb zig-cache/clashos-dbg -ex 'run target remote localhost:1234'
+```
+
+Note: this crashes GDB for me, but it works if I remove the `-ex`
+parameter and execute the command at the prompt.
+
 ### Actual Hardware
 
 1. Mount an sdcard with a single FAT32 partition.
@@ -48,3 +63,11 @@ For further changes repeat steps 3 and 4.
  * Black: Pin 6, Ground
  * Yellow: Pin 8, BCM 14, TXD / Transmit
  * Orange: Pin 10, BCM 15, RXD / Receive
+
+### How to view the serial data
+
+Where `/dev/ttyUSB0` is the device that represents the serial-to-USB cable:
+
+```
+sudo screen /dev/ttyUSB0 115200 cs8
+```