Add a User Guide for experienced CsvReaders

[zaleslaw]

Inspired by discussion here #998 (comment) I recognized that we need a couple of Guides (targeted for both, humans and AI) regarding our operations and nuances of CSV reading, parsing edge cases, converting types and so on

Let's brainstorm a plan for that and you could implement it

[Jolanrensen]

good idea! Though, scratch "converting types" as that's not part of CSV parsing.