Update README.md

Signed-off-by: Lee Calcote <lee.calcote@layer5.io>

Author: leecalcote

README.md

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 # Introduction to Istio
-A workshop teaching concepts of service mesh through the lens of Istio. Questions? See the community [discussion forum](http://discuss.layer5.io).
+A workshop teaching concepts of service mesh through the lens of Istio. Questions? See the community [discussion forum](https://discuss.layer5.io).
 
 [Free] Use the Cloud Native Playground to walk-through the labs in this workshop in a live Kubernetes environment - https://play.meshery.io