Update ubuntu installation instructions

[philn]

https://wpewebkit.org/about/get-wpe.html refers to some now-removed ubuntu packages. We should either recommend the debian pkgs or the unofficial snap from glancr folks.

[philn]

cc @bertogg ;)

[csaavedra]

What would be the appropriate recommendation? We need to be careful not to recommend something that might break people's systems and ideally test that it's possible first. Alternatively I'm OK with just removing Ubuntu from that list.

[bertogg]

If there is demand I can provide unofficial builds (PPA or similar), it's not necessarily a lot of work (depending on the architectures we want to support).

[csaavedra]

I am not aware of the reasons for it to have been removed from Ubuntu, but I am guessing low demand? If that's the case I don't think we need to provide them.

[bertogg]

I am not aware of the reasons for it to have been removed from Ubuntu

https://bugs.launchpad.net/ubuntu/+source/wpewebkit/+bug/1981592