Merge branch 'docs/add-aws-reference-diagram' into 'master'

Add in reference diagram for AWS arch

Closes gitlab-com/customer-success/professional-services#109

See merge request gitlab-org/gitlab-ee!3981

doc/university/high-availability/aws/README.md

@@ -26,6 +26,10 @@ Login to your AWS account through the `My Account` dropdown on
 Amazon Web Services console from where we can choose all of the services
 we'll be using to configure our cloud infrastructure.
 
+### Reference Architecture
+
+![Reference Architecture](img/reference-arch.png)
+
 ***
 
 ## Network