expand on how to fix typos

service/documentation.md

@@ -136,7 +136,18 @@ The [codespell][] program checks for spelling mistakes in CI. If you
 have a CI failure and you just want to get rid of it, try:
 
     apt install codespell
-    codespell --write-changes $affected_file.md
+
+And then:
+
+    codespell --interactive 3 --write-changes $affected_file.md
+
+Or just:
+
+    codespell -i 3 -w
+
+... to check the entire wiki. Eventually, we *do* aim to fix all the
+typos, but there's over a hundred of them at the time of writing, so
+we only fail on changed files for now.
 
 ## Accepting merge requests on wikis