Make install instructions on readme much easier

[mszell]

Once conda-forge is done #80 , show the "easy way" installation with one line of conda, as here, and all the environment/pixi way in a collapsed/advanced section. To reach the broadest possible audience.

[mszell]

Have split it up in #109 , but the advanced part could be moved into a docs section, as here, to not take up too much space in the readme.

[mszell]

Until dependencies are not installed #111 , make clear they need to be installed too (and how)