Show a more helpful error message if the user tries to run the installer on Linux (not macOS)

[rxhfcy]

If someone tries to launch the installer from Linux (not macOS) for some reason, here's what currently happens:

$ curl https://alx.sh | sh
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100  1588  100  1588    0     0   1371      0  0:00:01  0:00:01 --:--:--  1371

Bootstrapping installer:
  Checking version...
  Version: v0.6.4
  Downloading...
  Extracting...
  Initializing...

The installer needs to run as root.
Please enter your sudo password if prompted.
sh: line 58: exec: caffeinate: not found

Instead of somewhat confusingly complaining about caffeinate, detect the platform (ARM64 Linux) and show a more helpful error message instead: "Looks like you're trying to run the installer from Linux. Boot to macOS and run the installer from macOS." or something like that.

• Also add an additional error for people who are running on x64 Linux for some reason? ("Sorry, Asahi Linux only supports Apple Silicon machines.")

Somewhat related: you've already added similar more helpful error messages for trying to run on an Intel Mac, trying to use a macOS version that is too old, and running the installer under Rosetta.