Add docs and tutorials

[moigagoo]

Karax looks like a cool project and I would like to use it, but there are barely any docs and no getting started guide.

[Araq]

So read the code of the example applications? Better docs would always be nice of course, but the examples work and are not big, you can read them line by line.

[Araq]

Now we have https://nim-lang.org/araq/karax.html

Closing. :-)