update build commands

Author: avivace

unbricked/serial-link/build.sh

@@ -1,5 +1,6 @@
 #!/bin/sh
 
+rgbasm -o sio.o sio.asm
 rgbasm -o main.o main.asm
-rgblink -o unbricked.gb main.o
+rgblink -o unbricked.gb main.o sio.o
 rgbfix -v -p 0xFF unbricked.gb