Add Log4j advisory in the README (#671)

* Add Log4j advisory on README

* Tweak advisory

README.md

@@ -5,6 +5,10 @@
 
 ![Continuous Integration](https://github.com/GoogleCloudPlatform/microservices-demo/workflows/Continuous%20Integration%20-%20Master/Release/badge.svg)
 
+> **⚠ ATTENTION: Apache Log4j 2 advisory.**  
+> Due to [vulnerabilities](https://cloud.google.com/log4j2-security-advisory) present in earlier versions
+> of Log4j 2, we have taken down all affected container images. We highly recommend all demos and forks to now
+> use images from releases [>= v0.3.4](https://github.com/GoogleCloudPlatform/microservices-demo/releases).
 
 **Online Boutique** is a cloud-native microservices demo application.
 Online Boutique consists of a 10-tier microservices application. The application is a
@@ -22,8 +26,6 @@ If you’re using this demo, please **★Star** this repository to show your int
 > [go/microservices-demo](http://go/microservices-demo) if you are using this
 > application.
 
-Looking for the old Hipster Shop frontend interface? Use the [manifests](https://github.com/GoogleCloudPlatform/microservices-demo/tree/v0.1.5/kubernetes-manifests) in release [v0.1.5](https://github.com/GoogleCloudPlatform/microservices-demo/releases/v0.1.5).
-
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