Add helm-docs to pre-commit (nginx#2230)

Problem: helm-docs wasn't working correctly with pre-commit when we
started using it, but now it's fixed

Solution: Add helm-docs to pre-commit now that it works

.pre-commit-config.yaml

@@ -67,7 +67,16 @@ repos:
     rev: v2.2.0
     hooks:
       - id: doctoc
-        args: [--update-only, --title, '## Table of Contents']
+        args: [--update-only, --title, "## Table of Contents"]
+
+  - repo: https://github.com/norwoodj/helm-docs
+    rev: v1.14.2
+    hooks:
+      - id: helm-docs-built
+        args:
+          - --chart-search-root=charts
+          - --template-files=_templates.gotmpl
+          - --template-files=README.md.gotmpl
 
 ci:
   skip: [golangci-lint-full, prettier, markdownlint-cli2, yamllint]