Update elementary OS instructions for 5.1+

[cassidyjames]

As of elementary OS 5.1 up-to-date Flatpak is included in the repo and preinstalled, AppCenter supports Flatpak ootb, and the preinstalled Sideload app handles .flatpakref files. Since 5.0 users are upgraded to 5.1 and older versions are EOL, there's no need for older instructions.

Installing an app from a .flatpakref with Sideload also adds its remote, so there's no need to add it separately.

I also tweaked the language for talking about Flathub, since curated AppCenter apps will be moving to use Flatpak by default from the elementary AppCenter remote, so users just wanting to get "Flatpak" on elementary OS will already have it. But this still directs them to Flathub for what elementary refers to as "non-curated" apps.

[TingPing]

I think the Flathub section should remain as-is just to be consistent and clear.

[cassidyjames]

@TingPing it's completely unnecessary (and very non-elementary) to direct users to the Terminal, though. It makes it seem more complicated to add Flathub than it really is.

[TingPing]

The problem is you made a circular reference that doesn't help the user.

flatpak.org setup says "go to flathub" -> flathub.org setup says "see flatpak.org".

You can document the graphical workflow if you prefer linking to the .flatpakrepo file directly.

[cassidyjames]

@TingPing I don't see how anything I did is circular. The setup guide amounts to: you're already set up, go install stuff. It's not substantially different than PureOS except manually adding the repo is not needed so you can just go install stuff. And nearly every OS's instructions link to Flathub at the end so I was keeping that at least somewhat consistent.

Clicking the big "Install" button on Flathub already links to the .flatpakrepo which works correctly on elementary OS. Documenting that seems entirely convoluted.

If you'd prefer, I can echo the Linux Mint instructions and just say that Flatpak is already set up and ready to go in elementary OS instead.

[TingPing]

Mint has Flathub pre-configured that is why it is omitted. elementary does not so I think it is valuable to say how. (And no the normal install button is not the same as adding a repo normally. Again you can just link to the repo file.)

[TingPing]

Tell users to hit the big obvious button

I don't understand why you are so against users just adding the repo. Surely you understand the workflow is entirely different than installing an app from the website.

[cassidyjames]

@TingPing because telling people to open Terminal means we've already failed. And it is not needed on elementary OS, since Sideload does that automatically when installing an app. There is no need to add extra steps—especially ones involving Terminal—for elementary OS users.

If at some point Sideload handled .flatpakrepo files as well we could direct users to do that (like the PureOS directions), but that's not the case today, and using Sideload is the recommended way to get Flatpaks.

[TingPing]

OK, sideload doesn't support repo files is all you had to say. I think this is still a bad solution but oh well.