docs: Added ArgoCon 21 presentation (argoproj#1811)

Signed-off-by: Kostis Kapelonis <[email protected]>

Author: kostis-codefresh

README.md

@@ -62,5 +62,6 @@ To learn more about Argo Rollouts go to the [complete documentation](https://arg
 * [GitOps with Argo CD and an Argo Rollouts canary release](https://www.youtube.com/watch?v=35Qimb_AZ8U)
 * [Multi-Stage Delivery with Keptn and Argo Rollouts](https://www.youtube.com/watch?v=w-E8FzTbN3g&t=1s)
 * [Gradual Code Releases Using an In-House Kubernetes Canary Controller on top of Argo Rollouts](https://doordash.engineering/2021/04/14/gradual-code-releases-using-an-in-house-kubernetes-canary-controller/)
+* [How Scalable is Argo-Rollouts: A Cloud Operator’s Perspective](https://www.youtube.com/watch?v=rCEhxJ2NSTI)