Added kapp notes to the knowledge base

knowledge base/kapp.md

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+# Kapp
+
+## TL;DR
+
+```shell
+# Configurations picked up from a directory
+$ kapp deploy -a my-app -f ./examples/simple-app-example/config-1.yml
+
+# Can be used with helm charts, removing need for Tiller
+$ kapp -y deploy -a my-chart -f <(helm template my-chart --values my-vals.yml)
+
+# … and with kustomize
+$ kapp -y deploy -a my-app -f <(kustomize build ./my-app)
+
+# … or templated with ytt
+$ kapp -y deploy -a my-app -f <(ytt -f ./examples/simple-app-example/config-1.yml)
+```
+
+## Further readings
+
+- Official [website]
+
+[website]: https://get-kapp.io