Create a tutorial for newcommers

[Danielduel]

As a user of more mainstream desktop environments I think this project would benefit from a quick-start guide/tutorial for people who try tiling manager for the first time.

Initial changes: Those things can be learned from reading config file, but I believe that letting user play around with vivarium without digging into docs would be a huge plus:

• alacritty should be mentioned in dependencies with a note that user can reconfigure default program in config
• alt(meta)+shift+return should be mentioned as a default way to create a new window, maybe it would be worth noting that in some parts of the world "return" is called "enter"

// Edit - I did an error in "new tile" keypress combination

[Danielduel]

As a starter, I did a sketch of such guide, tried to make it in the way that slowly introduces new concepts https://github.com/inclement/vivarium/pull/111