EKS content added

[PetrMc]

the following details are added:

• EKS Addon deployment steps (UI and CLI - previously only CLI was covered)
• details on installing Istio Gateway after EKS addon is created in the cluster

[PetrMc]

added it to overcome an issue with Netlify. The issue is resolved via https://github.com/tetratelabs/istio-distro.io/pull/280