doc: add warning based on wkhtmltopdf recommendations

Author: Arthurlbc

README.md

@@ -25,6 +25,16 @@ composer require knplabs/knp-snappy
 
 ## Usage
 
+> ⚠️ **Security Warning: Do NOT use `wkhtmltopdf` with untrusted HTML!**
+>
+> Never process user-supplied HTML/JS without **thorough sanitization**.  
+> Failing to do so can result in a **complete takeover of the server** running `wkhtmltopdf`.
+>
+> To mitigate risks, it is strongly recommended to use a Mandatory Access Control system like **AppArmor** or **SELinux**.
+>
+> 🔗 [See the official recommendations](https://wkhtmltopdf.org/status.html#recommendations)
+
+
 ### Initialization
 ```php
 <?php