Add Gentoo Prefix vs Nix comparison in documentation

[vanzod]

Currently there is no documentation on why the project has chosen Gentoo Prefix over Nix. This would be useful information to retain.

A few notes on the topic from a Slack conversation with Bart Oldeman at Compute Canada:

• Nix does not provide a good development platform when used via environment variables. A better option would be to use nix-shell, but that would require users to learn how to use it. For example, see https://github.com/NixOS/nixpkgs/issues/44144.
• The lower number of symlinks and the ability to use $EPREFIX/etc/ld.so.cache with Gentoo Prefix might improve overall performance thanks to the lower overhead for the dynamic linker/loader $EPREFIX/lib/ld-linux-x86-64.so.2 to locate the required dynamic libraries.

[boegel]

@bartoldeman Anything you have to add here?

[bartoldeman]

Looks ok but could elaborate a bit more, by adding a reference to https://github.com/NixOS/nixpkgs/issues/44144 and for "the linker" you can be more specific and say "the dynamic linker/loader $EPREFIX/lib/ld-linux-x86-64.so.2"

[vanzod]

@bartoldeman, thanks for the feedback. I have updated my comment.