Add a deprecation notice (#92)

* update readme with deprecation notice
* Update README.md

---------

Co-authored-by: Manuel Recena <[email protected]>

Author: diogoasouza

README.md

@@ -1,4 +1,8 @@
 # Istio Installer
+
+> [!NOTE]  
+> The [rancher-istio chart](https://github.com/rancher/charts "rancher-istio chart") will be deprecated starting on Rancher 2.12.0. For more information, see the [announcement](https://forums.rancher.com/t/deprecation-of-rancher-istio/45043) in the Rancher forums.
+
 This image is used by the [rancher-istio chart](https://github.com/rancher/charts "rancher-istio chart") to intall istio with various configurations.
 
 This installer uses shell scripts to run istioctl install, upgrade and uninstall commands.