service/documentation: add pre-commit hook bit

service/documentation.md

@@ -156,6 +156,12 @@ could start an "exclude file" (`exclude-file = PATH` in the
 Some file patterns are skipped in the `.codespellrc` (currently
 `*.json`, `*.csv`, and the entire `.git` directory).
 
+You can also add this to a `.git/hooks/pre-commit` shell script:
+
+    codespell $(git diff --cached --name-only --diff-filter=ACM)
+
+This will warn you before creating commits that fail the codespell check.
+
 ## Accepting merge requests on wikis
 
 It's possible to work around the [limitation of Wiki permissions](https://gitlab.torproject.org/tpo/tpa/gitlab/-/issues/76)