�doc: add short advice for authentication to readme

README.md

@@ -86,7 +86,7 @@ $ pip install bardapi==0.1.23a
 <br>
 
 ## Authentication
-> **Warning** Do not expose the `__Secure-1PSID` 
+> **Warning** Do not expose the `__Secure-1PSID`. For testing purposes only; avoid direct application use. Cookie values change periodically (every 15-20 minutes). Frequent session changes may briefly block access; headless mode is challenging. Rate limiting applies and changes often. If the cookie changes, log out of your Google account, close the browser, and enter the new cookie value. Or manually reset the cookie for a new value. See FAQ and issue pages for details.
 1. Visit https://bard.google.com/
 2. F12 for console
 3. Session: Application → Cookies → Copy the value of  `__Secure-1PSID` cookie.