Update instructions for Apple Silicon macs

[fredsa]

Partially addresses outdated instructions mentioned in #58

[fredsa]

To note, I'm not sure what the 7800 steps are, so those would need to be added to README-macos.md.

Would appreciate some help with those.

I got as far as:

git clone git@github.com:7800-devtools/7800basic.git
cd 7800basic
sed -i -e 's/dos2unix/tr -d "\\r" </' makepackages.sh
sed -i -e 's/unix2dos/tr "\\r?\\n" "\\r\\n" </' contrib/src/make_libraries_adhoc_static.sh
make

Unfortunately, the build is missing contrib/Darwin.arm64/… so the build fails here:

cc  -o 7800basic 7800bas.c statements.c keywords.c minitar.c -Lcontrib/adhoc/lib -Icontrib/adhoc/include -lpng -lz -lm -llzsa
statements.c:17:10: fatal error: 'shrink_inmem.h' file not found
   17 | #include <shrink_inmem.h>

Filed 7800-devtools/7800basic#25