Documentation improvements

[SolarDrew]

The docs are laid out roughly in accordance with the diataxis philsophy. There are a few places where this could be better, and a few where coverage of important topics can be improved. A non-exhaustive list:

• remove extraneous explanation and side-quests from the tutorials to give a more focused flow
• move those extra bits of explanation into the topic guides section
• add a "Working with a VBI Dataset" tutorial
• add a How-To Guides section

[Cadair]

Also adding some more short specific example like tutorials, starting with what we did on the last day of the workshop would be good.