readme: graphic mode arm link to stack overflow question

Author: cirosantilli

README.adoc

@@ -293,6 +293,8 @@ cat /dev/urandom > /dev/fb0
 ....
 * have a look at `./run -a arm` at 2852fe1989a6f1ab546e9a4fa88724423b3949f5 which is before we moved to `-M virt`
 
+Related: https://stackoverflow.com/questions/20811203/how-can-i-output-to-vga-through-qemu-arm
+
 ==== Graphic mode gem5
 
 https://stackoverflow.com/questions/50364863/how-to-get-graphical-gui-output-and-user-touch-keyboard-mouse-input-in-a-ful/50364864#50364864