Support arm64 on Linux/FreeBSD/OpenBSD

[hartraft]

Hi I was trying to install this on an arm64 Linux device but the following install.sh script failed.

$ curl -sfL https://raw.githubusercontent.com/knipferrc/fm/main/install.sh | sh
knipferrc/fm crit platform linux/arm64 is not supported. Make sure this script is up-to-date and file request at https://github.com/knipferrc/fm/issues/new

I see that Issue #96 Support M1 has been resolved and that Darwin and other arm64 targets are released. So I did a naive PR to add these targets to the install.sh script.