Improve docs with recommended use cases for novice users

[nyurik]

A common type of questions for Martin is when to use what, and in what way. We need an intro section in the book that covers:

• Concept of a base map vs "the story" data layers
• Explain that creating tiles on the fly from a DB is usually too slow for the base map, but good for the data layers
• Recommends planetiler as a way to pre-generate base map
• Mention serving from pmtiles/mbtiles
• Mention nginx proxy as a good way to combine tile serving and static file serving (i.e. web site)
  ...?