Install Postgres via Hombrew bottle

Upstream maintainers put thought into what is
and what isn't sensible to include by default.
Those decisions establish a de facto standard
that is broader in scope than Laptop:
Homebrew users, library users, etc.

The further we stray from the defaults,
the more likely we are to run into problems,
and those problems will be harder.

The most widely experienced, most urgent,
and most rapidly fixed problems will be
problems with installing using formula defaults.
Problems from using non-defaults are relatively lonely.

Also, Homebrew bottles are awesome:

https://github.com/Homebrew/homebrew/wiki/FAQ#why-do-you-compile-everything

Using options forces an install from source rather than a bottle,
which is much, much slower:

> Options were passed to the install command i.e. `brew install
> $FORMULA` will use a bottled version of `$FORMULA`, but `brew install
> $FORMULA --enable-bar` will trigger a source build.