Update "Debian Backports" link to Debian Wiki

Debian Backports is now an official service.
Improve the readme
Remove Installation chapter from the readme

This cookbook is now going to be the community site version, so prefer
normal installation and do not encourage using git version.
Merge branch 'readme'
Release v1.4.0

Minor version bumb to celebrate the first community site release.

Huge thanks and respect to Guilhem Lettron (https://github.com/guilhem)
for giving the community site cookbook name for us.