Révision quickstart, ajout packages Debian, liens, petites corrections

[Krysztophe]

• Added reference on existing Debian packages
• I've tried to distinguish clearly what is possible through packages and what must be done manually
• titles more explicit
• references to hypopg where forgotten
• links to manual installation
• small typos, minor wording changes
• replaced 9.4 by 9.6

[rjuju]

Thanks!