update README

Author: raesene

README.md

@@ -2,14 +2,15 @@
 
 This is just a small program that can be used to create and approve a Client Signing Request in a Kubernetes cluster and then create a new kubeconfig based on that approved certificate.
 
-The code is heavily based on [this article](https://medium.com/@elfakharany/automate-kubernetes-user-creation-using-the-native-go-client-e2d20dcdc9de) with some modifications for new CSR API versions and things I needed for this example.
+The code is heavily based on [this article](https://medium.com/@elfakharany/automate-kubernetes-user-creation-using-the-native-go-client-e2d20dcdc9de) with some modifications for new CSR API versions and things I needed for this example. Setting `expirationSeconds` will add that to the CSR. Kubernetes servers tend to have upper limits for how long they'll issue a certificate for (although these times vary wildly), and generally `600` is the lower bound for what you can set.
 
-It works based on the current context in a provided Kubeconfig file. If no file is provided then $HOME/.kube/config is used.
+It connects to a cluster based on the current context in a provided Kubeconfig file. If no file is provided then $HOME/.kube/config is used.
 
-There are three command line parameters
+There are five command line parameters :-
 
-* `--username` - The username for the certificate. This one is mandatory.
-* `--group` - The group for the certificate. Defaults to none.
-* `--kubeconfig` - The kubeconfig to use to connect to the cluster.
+* `--username` - The username for the certificate. (MANDATORY)
+* `--group` - The group for the certificate. Defaults to none. (OPTIONAL)
+* `--kubeconfig` - The kubeconfig to use to connect to the cluster. Default is `$HOME/.kube/config` (OPTIONAL)
+* `--output-file` - Filename for the output kubeconfig file. Default is [username].config (OPTIONAL)
+* `--expirationSeconds` - Number of seconds for the certificate to be valid.  If not specified this will take the server's default setting.  (OPTIONAL)
 
-The Kubeconfig file will have the filename of the user provided.