pre-commit: add qhelp check

Also the instructions on customizing `pre-commit`'s behaviour have been
updated to use the `--config` option.

.pre-commit-config.yaml

@@ -7,6 +7,7 @@ repos:
     hooks:
     -   id: trailing-whitespace
     -   id: end-of-file-fixer
+
 -   repo: local
     hooks:
     -   id: codeql-format
@@ -14,8 +15,15 @@ repos:
         files: \.qll?$
         language: system
         entry: codeql query format --in-place
+
     -   id: sync-files
         name: Fix files required to be identical
         language: system
         entry: python3 config/sync-files.py --latest
         pass_filenames: false
+
+    -   id: qlhelp
+        name: Check query help generation
+        files: \.qhelp$
+        language: system
+        entry: python3 misc/scripts/check-qhelp.py