README: Remove outdated AUR package

efa has been packaged as

[libtravel-routing-de-vrr-perl](https://packages.debian.org/search?keywords=libtravel-routing-de-vrr-perl)

for Debian, so you can install it using your package manager of choice on

Debian-based Linux distributions. It is also available as

[perl-travel-routing-de-vrr-git](https://aur.archlinux.org/packages/perl-travel-routing-de-vrr-git/)

in the archlinux User Repository (AUR). Both provide the commandline client and

the Perl module.

Debian-based Linux distributions. The package provides the commandline client

as well as the Perl module.

If you are using another distribution or would prefer a more recent version,

you have four installation options: