docs(nginx-system): Add intial README

infrastructure/nginx-system/README.md

+nginx-system
+===
+
+This component provides `ingress-nginx` as ingress solution to the cluster. It comes with some improved defaults, e.g. deploying a WAF by default.
+
+Links
+---
+
+- [Docs](https://kubernetes.github.io/ingress-nginx/)
+- [Helm Chart](https://artifacthub.io/packages/helm/ingress-nginx/ingress-nginx)
+