Update docs about how Calva finds the project root

[bpringe]

From a discussion in Slack, @PEZ said we should probably try to describe how the project root is determined on this page: https://calva.io/workspace-layouts/, and link to it from the connect page.

This came from a question about jack-in not working. The user had a file structure open in vs code that did not have a deps.edn file at the root.

If you have a structure like this:

- foo
  - bar
    - deps.edn
    - src
      - baz.clj

... having baz.clj open, jack-in should work.

We should update the note on this page: https://calva.io/connect/