Add installation guide and fix demo gif

[MattTree]

No description provided.

[MattTree]

The guide will avoid moments like, "Wait do I have to use a lua interpreter?" and "What's openal32.dll?"

[rgrams]

Hey, thanks for the PR.

• Does it complain about missing openal32.dll for you? That's my bad. That's the sound library, and since I disabled the sound module, I figured it wouldn't need it, and it works just fine without it on my machine (I must have OpenAL installed though). I can fix the release to include it, you shouldn't have to download it separately.
• Did the link to the demo gif not work for you, or you just think it's better to embed it?

[MattTree]

heya

• Yeah it complained about missing openal32.dll for me.
• I think it's better to embed the gif. It communicates the essence faster. If you think the gif is too intense then I would at least have a static image.

If you agree with any of the changes it might be better for you to manually do them in one commit to avoid having so many. I messed up and needed multiple.