Make the security warning more obvious

README.md

@@ -54,7 +54,8 @@ echo $converter->convert('# Hello World!');
 
 Please note that only UTF-8 and ASCII encodings are supported.  If your Markdown uses a different encoding please convert it to UTF-8 before running it through this library.
 
-🔒 If you will be parsing untrusted input from users, please consider setting the `html_input` and `allow_unsafe_links` options per the example above. See <https://commonmark.thephpleague.com/security/> for more details. If you also do choose to allow raw HTML input from untrusted users, consider using a library (like [HTML Purifier](https://github.com/ezyang/htmlpurifier)) to provide additional HTML filtering.
+> [!CAUTION]
+> If you will be parsing untrusted input from users, please consider setting the `html_input` and `allow_unsafe_links` options per the example above. See <https://commonmark.thephpleague.com/security/> for more details. If you also do choose to allow raw HTML input from untrusted users, consider using a library (like [HTML Purifier](https://github.com/ezyang/htmlpurifier)) to provide additional HTML filtering.
 
 ## 📓 Documentation