📝 add documentation about Skipper Ingress (#15)

Skipper Ingress Controller support is added with
fluxcd/flagger#670.

This commit add the documentation and links to mention
Skipper is now an available option.

Currently only Canary deployments are supported.

README.md

@@ -7,7 +7,7 @@ Flagger can run automated application analysis, testing, promotion and rollback
 * A/B Testing (HTTP headers and cookies traffic routing)
 * Blue/Green (traffic switching and mirroring)
 
-Flagger works with service mesh solutions (Istio, Linkerd, AWS App Mesh) and with Kubernetes ingress controllers (NGINX, Gloo, Contour).
+Flagger works with service mesh solutions (Istio, Linkerd, AWS App Mesh) and with Kubernetes ingress controllers (NGINX, Skipper, Gloo, Contour).
 Flagger can be configured to send alerts to various chat platforms such as Slack, Microsoft Teams, Discord and Rocket.
 
 ## Prerequisites