feat: update documentation

Author: edorizzardi

helm/oauth2-proxy/README.md

@@ -196,6 +196,7 @@ The following table lists the configurable parameters of the oauth2-proxy chart
 | `service.loadBalancerIP`                              | ip of load balancer                                                                                                                                                                                                                                              | `nil`                                                                            |
 | `service.loadBalancerSourceRanges`                    | allowed source ranges in load balancer                                                                                                                                                                                                                           | `nil`                                                                            |
 | `service.nodePort`                                    | external port number for the service when service.type is `NodePort`                                                                                                                                                                                             | `nil`                                                                            |
+| `service.targetPort`                                  | name for the service's `targetPort`                                                                                                                                                                                                                              | `""`
 | `serviceAccount.enabled`                              | create a service account                                                                                                                                                                                                                                         | `true`                                                                           |
 | `serviceAccount.name`                                 | the service account name                                                                                                                                                                                                                                         | ``                                                                               |
 | `serviceAccount.annotations`                          | (optional) annotations for the service account                                                                                                                                                                                                                   | `{}`                                                                             |
@@ -357,3 +358,6 @@ config:
     whitelist_domains = [ ".domain.com", ".example.io"]
     provider = "google"
 ```
+
+## Route requests to sidecar container
+You can route requests to a sidecar container first by setting the `service.targetPort` variable; by default, the service's `targetPort` value equals to the `httpSchema`'s.