Always use prompts for code snippets?

Hi there,

this is a followup to @norosa's comment:

> b) the `sh$` prompt was designed for consistency with the frequent use of `cr>` prompts in the main docs. we can revisit that decision if you like, but I think that should be done as a separate thing (perhaps with a PR to [crate-docs/style](https://github.com/crate/crate-docs/tree/main/style))

With kind regards,
Andreas.

_Originally posted by @norosa in https://github.com/crate/cratedb-examples/pull/3#discussion_r647563591_