Correct docs to suggest always using trailing slashes for directories with `--path-rename`

stitny~/r/nntplib (main)$ git --version
git version 2.35.1
stitny~/r/nntplib (main)$ git filter-repo --version
22826b5a68b6
stitny~/r/nntplib (main)$ git filter-repo --debug --path Doc/library/nntplib.rst --path Lib/nntplib.py --path Lib/test/test_nntplib.py --path-rename Doc/library: --path-rename Lib/test: --path-rename Lib:
[DEBUG] Passed arguments:
Namespace(analyze=False, blob_callback=None, commit_callback=None, debug=True, dry_run=False, email_callback=None, filename_callback=None, force=False, help=False, inclusive=True, mailmap=None, max_blob_size=0, message_callback=None, name_callback=None, no_ff=False, partial=False, path_changes=[('filter', 'match', b'Doc/library/nntplib.rst'), ('filter', 'match', b'Lib/nntplib.py'), ('filter', 'match', b'Lib/test/test_nntplib.py'), ('rename', 'match', [b'Doc/library', b'']), ('rename', 'match', [b'Lib/test', b'']), ('rename', 'match', [b'Lib', b''])], preserve_commit_encoding=False, preserve_commit_hashes=False, prune_degenerate='auto', prune_empty='auto', quiet=False, refname_callback=None, refs=['--all'], repack=True, replace_message=None, replace_refs=None, replace_text=None, report_dir=None, reset_callback=None, source=None, state_branch=None, stdin=False, strip_blobs_with_ids=set(), subdirectory_filter=None, tag_callback=None, tag_rename=None, target=None, to_subdirectory_filter=None, use_base_name=False, version=False)
[DEBUG] Migrating refs/remotes/origin/* -> refs/heads/*
[DEBUG] Removing 'origin' remote (rewritten history will no
        longer be related; consider re-pushing it elsewhere.
[DEBUG] Running: git fast-export --show-original-ids --signed-tags=strip --tag-of-filtered-object=rewrite --fake-missing-tagger --reference-excluded-parents --no-data --use-done-feature --mark-tags --reencode=yes --all
  (saving a copy of the output at .git/filter-repo/fast-export.original)
[DEBUG] Running: git -c core.ignorecase=false fast-import --force --quiet --date-format=raw-permissive
  (using the following file as input: .git/filter-repo/fast-export.filtered)
Parsed 1 commitsfatal: Empty path component found in input
fast-import: dumping crash report to .git/fast_import_crash_31798
Traceback (most recent call last):
  File "/usr/libexec/git/git-filter-repo", line 4004, in <module>
    main()
  File "/usr/libexec/git/git-filter-repo", line 4001, in main
    filter.run()
  File "/usr/libexec/git/git-filter-repo", line 3936, in run
    self._parser.run(self._input, self._output)
  File "/usr/libexec/git/git-filter-repo", line 1409, in run
    self._parse_commit()
  File "/usr/libexec/git/git-filter-repo", line 1260, in _parse_commit
    self._commit_callback(commit, aux_info)
  File "/usr/libexec/git/git-filter-repo", line 3483, in _tweak_commit
    if not self._prunable(commit, new_1st_parent,
  File "/usr/libexec/git/git-filter-repo", line 3239, in _prunable
    self._output.flush()
  File "/usr/libexec/git/git-filter-repo", line 2721, in flush
    self.file1.flush()
BrokenPipeError: [Errno 32] Broken pipe
stitny~/r/nntplib (main)$

Using openSUSE/Tumbleweed packages.

fast_import_crash_32751