Adding banner for v3

Author: leandrodamascena

docs/overrides/main.html

@@ -1,7 +1,7 @@
 {% extends "base.html" %}
 
 {% block announce %}
-🚨 RFC for <a href="https://github.com/aws-powertools/powertools-lambda-python/issues/4189">Powertools for AWS Lambda (Python) v3</a> is out!
+🚨 The next major version (v3) is coming - <a href="https://github.com/aws-powertools/powertools-lambda-python/issues/4189">come learn and discuss upcoming changes</a>!
 {% endblock %}
 
 {% block outdated %}