How best to help users add muse2 to their PATH?

[alexdewar]

If users go down the route of downloading a prebuilt binary for MUSE2 (as we expect most users to do -- building from source is pretty onerous), they will get a zip file with the muse2 executable and a README. Hopefully users will be familiar enough with the command line to know to run this program from the terminal with e.g. .\muse2.exe run C:\Users\Somebody\my_model or whatever (though maybe we shouldn't rely on this?). It is convenient to have muse2 on your PATH though so that you can just run muse2 run some_model from whatever directory you happen to be in. Manually adding things to your PATH is not totally trivial, though we could provide instructions on how to do this for different platforms.

I see a few options:

1. Provide instructions to users on how to do this manually, e.g. in the README files bundled with the binaries
2. Provide some kind of installer (if we want some inspo, maybe we should look at how other tools like GitHub CLI do it)
3. Add a command to muse2 itself to install it somewhere so that it appears on the user's PATH (on Linux you can just copy the file to ~/bin/, but it could be a real faff on Windows -- would need to look into this)

If we do #924 then maybe that's a good enough alternative.