Consider updating the docs for Dart Sass on Netlify to use Brewfile.netlify

[bep]

Consider updating the docs for Dart Sass on Netlify to use Brewfile.netlify

[jmooring]

If you are paying for build time...

$ time brew install sass/sass/sass

real	1m27.077s
user	0m46.632s
sys	0m35.418s


$ time curl -LJO https://github.com/sass/dart-sass/releases/download/1.63.5/dart-sass-1.63.5-linux-x64.tar.gz && tar -xf dart-sass-1.63.5-linux-x64.tar.gz

real	0m1.007s
user	0m0.132s
sys	0m0.033s

I'm not sure if brew installations are cached between builds.

It is also useful to be able to specify any version instead of what's available in the tap (e.g., roll back).

[bep]

Yea, right ...

I'll see if I can somehow get this into Netlify's (cached) setup.