* Update the instructions to reflect recent package availability
  * Nightly/stable packages for Ubuntu Xenial+Artful
  * Nightly/stable packages for Fedora 26+27
  * Remove references to Trusty as those are no longer being built
  * Remove references to Fedora 24 as those are no longer being built
Signed-off-by: Brenden Blanco <bblanco@gmail.com>