Warn about parsing user-generated HTML

src/PhpWord/Shared/Html.php

@@ -34,6 +34,8 @@ class Html
      * Add HTML parts.
      *
      * Note: $stylesheet parameter is removed to avoid PHPMD error for unused parameter
+     * Warning: Do not pass user-generated HTML here, as that would allow an attacker to read arbitrary
+     * files or perform server-side request forgery by passing local file paths or URLs in <img>.
      *
      * @param \PhpOffice\PhpWord\Element\AbstractContainer $element Where the parts need to be added
      * @param string $html The code to parse