Add metainfo

[orowith2os]

Necessary for most (or all) Linux builds. Needs some tweaking to be actually used, and a desktop file is necessary too.

[lexisother]

It's unlikely that it's up to your standards/expectations, but we have this currently:

[Desktop Entry]
Version=1.0
Type=Application
Name=ArmCord
Comment=Discord client for lower end ARM devices.
Exec=armcord
Icon=armcord
Categories=Internet;Network;InstantMessaging;

[orowith2os]

The desktop file is less of a problem, I can easily reuse it from the appimage or copy it elsewhere; if you want to push the desktop file here so it can be added in the packages though, it would be nice.

The metainfo will just kinda sit here, since other packages (like snap) don't use it, but instead generate their own things.