Fixes in 2020/ferguson1

Typo fix.

Rename COMPILING -> COMPILING.md and HACKING -> HACKING.md. I have not
tested the formatting on either of these but they should be okay.

Updated the COMPILING (portability information) as I know it works under
Apple M1 chips too.

2020/ferguson1/Makefile

@@ -420,7 +420,7 @@ MAY_NEED_GCC= gcc
 ##############################
 #
 OBJ= prog.o termcaps.o
-DATA= COMPILING HACKING bugs.md cannibalism.log \
+DATA= COMPILING.md HACKING.md bugs.md cannibalism.log \
     chocolate-cake.md crazy.log gameplay.md \
     snake-colours.sh snake.1 spoilers.md \
     termcaps.c terminals.md troubleshooting.md