INSTALL.md: add Macports option for macOS

[barracuda156]

hypre is supported in Macports for quite a while and regularly updated. Please consider adding it to install options (unless there is a policy not to add downstream options.)

It can be installed from Macports with sudo port install hypre.

We support macOS versions from Leopard to Sonoma, and all archs, including arm64 and ppc (ppc64 may not currently build for unrelated reasons, but hopefully that gets fixed too).