Update CHANGELOG.md with 0.5.0 changes

CHANGELOG.md

 # Changelog
 
+## [0.5.0] - 2020-09-17
+
+* Added automatic smtp config for nextcloud
+* Updated k3s version to 1.18.6+k3s1
+  * Updated kubernetes to 1.18.6
+* Updated applications:
+  * wordpress: 5.4.1
+  * nextcloud: 17.0
+  * flux: 1.20.2
+  * helm-operator: 1.2.0
+  * ingress-nginx: 0.35.0
+* Use metallb instead of servicelb in order to get ingress source IP and
+  allow IP based access controll
+* Allow second, custom flux instance
+* Allow k3s kubelet args
+* Allow custom extra values for helm charts
+* Added advanced installation docs
+* Separated ansible playbooks for Kubernetes and OpenAppStack (re-)installation
+* Increased installation and general stability
+
+
 ## [0.4.0] - 2020-06-11
 
 * Replaced [local-storage