Add small tutorial

[Ecostack]

A small tutorial on what are the important things to build in the first place would be great.
Frankly speaking, I got stuck after 1 minute.

[mlange-42]

I think having the players to figure out some stuff on their own is ok. But nothing speaks against writing a tutorial.

[mlange-42]

Started writing up some documentation. The tutorial could go there, too: https://github.com/mlange-42/tiny-world/tree/main/docs