Expanding platform support

Hi,

We are happy to now be able to support four different Nix platforms on nixbuild.net:

• x86_64-linux (supported since start)
• aarch64-linux (generally available a week ago)
• armv7l-linux (launched today!)
• i686-linux (launched today!)

All those systems are available to all our users, and priced identically. Configuring Nix for building additional systems on nixbuild.net is simple; just add additional remote builders to your Nix configuration.