F Infrastructure: documentation

[cmutel]

Documentation needs to be reworked and improved. A more decoupled organization of the Brightway 3 libraries should also make (new) contributions easier.

Specific tasks:

• F1 Develop new Sphinx template with a three column layout
• F2 Reorganize documentation following the Diataxis framework for technical documentation
• F3 Each notebook (where possible) should link to a try.brightway.dev container
• F4 Develop, document, and test contribution guidelines and coding styles, and apply to all libraries

[michaelweinold]

More than just completed, right, @cmutel? 😇