update readme

README.md

@@ -2,7 +2,7 @@
 
 Rolling Cluster Node Upgrades for AWS EKS
 
-**Project Status:** Work in progress and not ready for use at this moment. 
+**Project Status:** Used in production at Tenjin, some caveats apply.
 
 ## Use Case
 
@@ -14,3 +14,21 @@ In general terms:
 - Your cluster is made up of [EC2 Auto Scaling Groups (ASG)](https://docs.aws.amazon.com/autoscaling/ec2/userguide/AutoScalingGroup.html)
 - You want to replace one or all nodes in those ASGs (e.g. to [activate a new launch configuration](https://docs.aws.amazon.com/autoscaling/ec2/userguide/LaunchConfiguration.html))
 - The replacement has to be done gracefully, node-by-node, and respects [availability constraints in your cluster](https://kubernetes.io/docs/tasks/run-application/configure-pdb/)
+
+## Usage
+
+You can run this tool from your CI or locally. Typically we bundle it as a script and inject secrets within the CI.
+
+Example using standard AWS SDK credentials and an assumed role:
+
+```bash
+#!/bin/bash
+set -ex
+docker run --rm -it \
+    -e ACCESS_KEY_ID=${ACCESS_KEY_ID:?}
+    -e SECRET_ACCESS_KEY=${SECRET_ACCESS_KEY:?}
+    -e ROLE_ARN=${ROLE_ARN:?}
+    -e CLUSTER=your-cluster-name \
+    -e AUTOSCALING_GROUPS=${AUTOSCALING_GROUP:?} \
+    rotate-eks-asg:latest
+```