Add a 'beginner tips' dialog

[gsass1]

Something similar to what you get when you first install Adobe Acrobat Reader.

We could add some simple descriptions and some screenshots. Mostly about how you can get new mods (through the site button).

[dd86k]

I agree to this.

[dd86k]

I'll add a '?' button because 10/10 design

[dd86k]

For now, a single or a few web pages can be done on the official website, the help button would simply open that.