Adding an appdata.xml

[andy5995]

There was some discussion about this in #2093

https://www.freedesktop.org/software/appstream/docs/chap-Quickstart.html#sect-Quickstart-DesktopApps

Is there a final verdict on whether or not an appdata.xml should be included?

[elextr]

Well, @b4n said on #1142 "I basically hate everything that tries and put the upstream (us) in downstream's (distributions) place. It's not our role, and a lot of upstream trying to be "smart" and "help" downstream just end up with a terrible mess that just make everyone's lives harder." See also further rants on #1142.

And regarding images I said on #2014 "For example I just updated to the latest Mint and found icons are provided for save all and build so Geany's fallback "blue floppy disk stack" and "red fallen over bookcase" icons don't show, but they have on every other distro I've used (including older mints) and stand out like [colloquial expression elided] on "modern" flat dark themes."

My summary of previous discussions would be:

a) to be distro independent its going to be pretty bland, carefully can't mention Gnome/KDE/Mint/Nixos or whatever.
b) since theming is delegated to the distro, Geany doesn't know what it will look like, so images are pretty sure to be wrong on any but the originator's system, so I guess photos on my dark theme Mint should be used so it doesn't look like any other distro 😁
c) not sure how happy translators are going to be with more work that may or may not be used by distros (@frlan thoughts?).

So if there is any verdict its not positive so far.