Add to compiling instruction for non-standard builds to README (e.g. macOS - emacsformacos)

[ed9w2in6]

Hi, I use a build from emacsformacos and the Emacs installation structure is non-standard for its build.

FWIW, to compile hotfuzz on such non-standard setup one will need to set the environment variable
EMACS_ROOT to the root directory of Emacs (i.e. the directory contains the include/, lisp/, site-lisp/, etc.)

For emacsformacos, one should set to it to EMACS_ROOT to '/Applications/Emacs.app/Contents/Resources/'.

Maybe these information should be added to README.

[ed9w2in6]

An unrelated note to this issue:
I had also adopted commits from #13 , which allows consult to use hotfuzz in more situations. I think it can be merged.

[jwr]

As a data point, I built the provided module on MacOS using the default instructions:

mkdir build
cd build
cmake -DCMAKE_C_FLAGS='-O3 -march=native' .. \
	&& cmake --build .

and it worked right away. I'm using emacs-mac from the homebrew railwaycat/emacsmacport tap.

I also had to use the defadvice workaround to make hotfuzz work with consult.