Add description about local http proxy setting's effect on liveness p…

…robe

content/en/docs/tasks/configure-pod-container/configure-liveness-readiness-probes.md

@@ -173,6 +173,10 @@ the Container has been restarted:
 kubectl describe pod liveness-http
 ```
 
+Before and in v1.13, if `http_proxy` or `HTTP_PROXY` environment variables was set on the
+node which pod is running, the http liveness probe would use that proxy. After v1.13, local
+http proxy envirnment variables would not effect http liveness probe any more.
+
 ## Define a TCP liveness probe
 
 A third type of liveness probe uses a TCP Socket. With this configuration, the