Merge pull request #4442 from Refutable4890/copy-doc

Add a description of the resumption of `copy`

doc/045_working_with_repos.rst

@@ -136,6 +136,8 @@ or the environment variable ``$RESTIC_FROM_KEY_HINT``.
     repository. You can avoid this limitation by using the rclone backend
     along with remotes which are configured in rclone.
 
+.. note:: If `copy` is aborted, `copy` will resume the interrupted copying when it is run again. It's possible that up to 10 minutes of progress can be lost because the repository index is only updated from time to time.
+
 .. _copy-filtering-snapshots:
 
 Filtering snapshots to copy