Fix incorrect kart reset hint in status responses.

[hamishcampbell]

Kart v0.9.1.dev0+ci.2237.git0e0a8ed3, Copyright (c) Kart Contributors
» GDAL v3.2.0; PROJ v6.3.0
» PyGit2 v1.3.0; Libgit2 v1.1.0; Git v2.31.1
» SQLAlchemy v1.4.11; pysqlite3 v2.6.0/v3.31.1; SpatiaLite v5.0.0; Libpq v13.0.2
» SpatialIndex v1.9.3

If you have uncommitted working copy changes and use status you will a message like so:

$ kart status
On branch main

Changes in working copy:
  (use "kart commit" to commit)
  (use "kart reset" to discard changes)
...

However kart reset does not work here.

$ kart reset
Usage: kart reset [OPTIONS] REFISH
Try 'kart reset --help' for help.
Error: Missing argument 'REFISH'

IIRC reset was re-worked to match the equivalent Git command, and the correct message here should be:

use "kart restore" to discard changes.