Sorry! Someone already filed an issue about this [1], but I haven't had time to investigate exactly what is appropriate to put there. I don't use Linux, nor have I ever released and distributed open-source software before, so I'm just kinda guessing here -- other people have added the project to various package managers, not me.
Installing via Linux Homebrew is simply listed as an option because it's available as a Homebrew formula. And the option to install via cargo is also noted.