Improve the usability of the Local Users guide (#12001)
Improve the usability of the Local Users guide (#12001)

* Improve the usability of the Local Users guide

See #11841

- Define "local users" at the beginning of the guide
- Split the "Adding and deleting users" section and move the "Deleting
  users" section after the "Editing users" section. This way, readers
  can follow all commands in the guide. Otherwise, the new user is
  deleted before being edited.
- Hide scope-irrelevant details
- Remove a "tsh ssh" command that a reader may not necessarily have
  set up Teleport to run properly.

* Respond to PR feedback
gravitational/teleport,gravitational/teleport,gravitational/teleport,gravitational/teleport,gravitational/teleport,gravitational/teleport