Cover the macOS installer and crates.io in INSTALL.md
Cover the macOS installer and crates.io in INSTALL.md

Extend the installation instructions to cover the upcoming installation
methods once we have a formal release.  In particular, detail the pkg
file we will supply for macOS and the ability to build straight from
crates.io.

bazelbuild/sandboxfs,bazelbuild/sandboxfs,bazelbuild/sandboxfs