[linux appimage] Doesn't work without installed sdl2 libraries

[Amlor]

Should probably bundle SDL2* into the appimage

[dalerank]

Can we add .so in image?
Or better use static link instead?

[Amlor]

I'll look into it

[Amlor]

Okay, so I checked it out a bit more and have realized that it's not, in fact, and AppImage, just the main executable.
AppImages are more alike to mac apps, they can be mounted like a disk and have an internal file tree.

What I will do next:

1. Update readme with instructions to install dependencies. Clarify build names to reflect what is actually produced.
2. Try to create rpm/deb (arch linux AUR?) packages that will install their dependencies automatically
3. Create an actual AppImage