The command to run had a typo in the pathname which prevented copy
pasting it to work, which has annoyed me enough to fix this now.
# 3. Run the cleanup script and let it sort the entries and remove unused
# references from lines you removed in step (2):
#
-# $ ./script/release-notes.pl cleanup
+# $ ./scripts/release-notes.pl cleanup
#
# 4. Reload RELEASE-NOTES and verify that things look okay. The cleanup
# procedure can and should be re-run when lines are removed or rephrased.