[aur-general] Changes to AUR and community due to the multilib repository

With the creation of the [multilib] repository, all 32-bit libraries are now installed in /usr/lib32 and compiled from source using the gcc-multilib package instead of being copied from i686 packages. All AUR users maintaining lib32-* and bin32-* packages are encouraged to adapt their packages to the new layout. All trusted users who want to maintain 32 bit packages should join the arch-multilib mailing list and ask for access there. The x86_64 community repository should remain lib32-free in the future.