Update the installation page to acknowledge the unofficial snap package

[Protrikk]

Since a snap package is available for ubuntu, it'd be a good idea to recommend installing that instead of using a more conveluted way of adding repositories.

[DioEgizio]

It's not unofficial, but it's not stable yet (6.0 will have a stable snap I think)

[Lutitious]

Made a pr for this in #173 but only a draft for now as snap still isnt stable yet