docs/reference/builder: touch-up code-hints and some minor changes
docs/reference/builder: touch-up code-hints and some minor changes

- use "console" for code-hints, to make process output distinguishable
  from the commands that are executed
- use a consistent prompt for powershell examples
- minor changes in wording around "build context" to reduce confusion
  with `docker context`

Signed-off-by: Sebastiaan van Stijn <64b2b6d12bfe4baae7dad3d018f8cbf6b0e7a044@gone.nl>

thaJeztah/cli,docker/cli,cpuguy83/cli,thaJeztah/cli,docker/cli,cpuguy83/cli