[Feature Request] Add MacPorts as an installation method

Hi,

First off, thanks for this great tool. It's invaluable.

Is your feature request related to a problem? Please describe. I'm a Mac user. Since recently, I've had to use a Mac that has multiple user accounts. Due to limitations, Homebrew is not usable on a multi-user Mac environment. So I switched to MacPorts as the package manager for macOS.

Describe the solution you'd like Currently fvm is distributed via Homebrew. It would be great if you could make it available on MacPorts as well.

Thank you.