update readme with youtube image

Author: GordonBeeming

README.md

@@ -1,5 +1,7 @@
 # Building basic Azure infrastructure using Terraform
 
+[![](_docs/imgs/thumbnail.jpg)](https://www.youtube.com/watch?v=PNDSjqsBdmw)
+
 [video](https://www.youtube.com/watch?v=PNDSjqsBdmw)
 
 [blog post](https://devstarops.com/blog/blogs/dev/2022/8/building-basic-azure-infrastructure-using-terraform)