docs(k8up): Add intial README

infrastructure/k8up/README.md

+K8up
+===
+
+This component provides backup capabilities to the cluster. The backup repository and objects are namespaced, providing good isolation for all backups.
+
+
+Nice to knows
+---
+
+- This operator requires separate installation of CRD. This is currently not part of this module, which makes it essentially broken. Will be fixed down the line.
+
+Links
+---
+
+- [Docs](https://k8up.io)
+- [Helm Chart](https://artifacthub.io/packages/helm/appuio/k8up)
+- [Source Code](https://github.com/k8up-io/k8up)
+- [Forum](https://github.com/k8up-io/k8up/discussions)