add mac faq

[lijiarui]

add mac install Faq

[huan]

Oh BTW have a look at: https://github.com/zixia/node-facenet/blob/ee75f430ff58399e9526b0ef421dd3a1eee41347/.travis.yml#L23-L24

[lijiarui]

maybe we don't need brew update because when I trying install, it update automatically... shell like this:

➜  node-facenet git:(master) brew install pango
Updating Homebrew...

==> Auto-updated Homebrew!
Updated 1 tap (homebrew/core).
No changes to formulae.

==> Installing dependencies for pango: gobject-introspection, graphite2, harfbuzz
==> Installing pango dependency: gobject-introspection
==> Downloading https://homebrew.bintray.com/bottles/gobject-introspection-1.54.1.sierra.bottle.tar.g
######################################################################## 100.0%
==> Pouring gobject-introspection-1.54.1.sierra.bottle.tar.gz
🍺  /usr/local/Cellar/gobject-introspection/1.54.1: 173 files, 9.7MB
==> Installing pango dependency: graphite2
==> Downloading https://homebrew.bintray.com/bottles/graphite2-1.3.10.sierra.bottle.tar.gz
######################################################################## 100.0%
==> Pouring graphite2-1.3.10.sierra.bottle.tar.gz
🍺  /usr/local/Cellar/graphite2/1.3.10: 18 files, 259.3KB
==> Installing pango dependency: harfbuzz
==> Downloading https://homebrew.bintray.com/bottles/harfbuzz-1.5.1.sierra.bottle.tar.gz
######################################################################## 100.0%
==> Pouring harfbuzz-1.5.1.sierra.bottle.tar.gz
🍺  /usr/local/Cellar/harfbuzz/1.5.1: 137 files, 5.4MB
==> Installing pango
==> Downloading https://homebrew.bintray.com/bottles/pango-1.40.12.sierra.bottle.tar.gz
######################################################################## 100.0%
==> Pouring pango-1.40.12.sierra.bottle.tar.gz
🍺  /usr/local/Cellar/pango/1.40.12: 105 files, 4.5MB

Also, I haven't install libpng yet... Maybe it should be brew install pixman It seems it called pixman but I'm not sure, will keep on watching these package.