Return nightly builds and/or instructions to build on macOS

[jacksongoode]

See title

[kierandrewett]

We're working on building the browser to a point where it's useable before we can consider reintroducing builds.

As for macOS, we'll need to work on getting everything setup so we can compile for Mac. I imagine we'll have build instructions for other platforms (Windows included) very soon, especially as we get closer to having a stable browser 😄