Documentation on building with native-compilation

[alanshutko]

It would be nice if the readme had examples on how to build with the formula to enable native compilation or other features. I've only found examples in various Github Issues and while I had it working on Emacs 28, my first try with the formula today didn't work.

When I figure it out, I can propose documentation changes.

[alanshutko]

The two problems I found on a couple machine were needing to update gcc and libgccjit after updating command line tools, and creating the native-lisp symlink on a different machine. I'll work on a proposed doc update.