Additional installation instructions needed for macOS

[nzoghb]

In addition to needing to install the Rustlang toolchain, the build step requires the following dependencies:

$ brew install gnu-tar
$ brew install xz
$ brew install openssl

[ielashi]

@nzoghb It would be great it you could update the README with these instructions :)

[bitdivine]

Note: Dependencies are now installed by scripts/setup. That installs tar and xz but not openssl. I believe that we no longer need openssl for the build as openssl is now statically linked in the tooling that used to use it. As such, I think we can mark this ticket as closed.

The preferred way of building is now by docker, just for consistency. This works well on Linux and Intel Macs. We are however aware that there are problems using docker on M1 macs. Unfortunately it is hard to offer a reliable solution to this yet as there are no apple silicon runners on GitHub, so fixes get broken easily without anyone noticing. GitHub is due to offer apple silicon runners this Winter. I am looking forward to this, as then we can test our builds for M1 and get that working reliably.

[bitdivine]

Better link for the M1 runners on the GitHub roadmap: https://github.com/orgs/github/projects/4247/views/1?filterQuery=-status%3A%22Q4+2022+%E2%80%93+Oct-Dec%22+m1