Add flatpak-relevant files

[smirnov]

As requested in issue #403 I've created a flatpak package and in the package creation discussion it was suggested that I at the very least suggest putting the logo in PNG format and a desktop file with the source of the application, so here it is.

If you think that this is not useful or can suggest a better/alternative approach, I'm happy to hear it.

[coelckers]

You forgot "Shadow Warrior" in your list of keywords.

[madame-rachelle]

One thing I wonder is why this is needed for Raze but GZDoom doesn't have it and gets flatpaks published just fine. Though rather than dismissing this one, I'd prefer GZDoom to have a similar thing, instead.

[smirnov]

It's not "needed" as in "it won't be published if it's not there", as of right now Raze is on flathub. But it is a recommendation from Flathub to have those files upstream (and metadata, specifically for flatpak, forgot that one). If upstream doesn't agree, then the files are left in the flathub repo.

Maintainer for GZDoom has mentioned that their suggestion was rejected, flathub/flathub#5022 (comment) but if you see value in it - I'm happy to create PR for GZDoom as well (from what I can see the dev team is pretty much the same)

[QmwJlHuSg9pa]

You forgot "Shadow Warrior" in your list of keywords.

Adding to this, in GNOME Software, "duke nukem" returns no results, let alone "duke nukem 3d". Only "duke" or "nukem" individually present Raze in the search results.

[smirnov]

@QmwJlHuSg9pa thanks for the heads up. I see the 3d tag is missing, I'll fix that, but the "duke nukem" definitely returns results. Maybe a cache issue?