add kube academy prep course (#49)

- add Kube academy prep course

Author: walidshaari

README.md

@@ -270,6 +270,7 @@ complete -F __start_kubectl k
 
 - [Mumshad CKA with practice tests and mock exams](https://www.udemy.com/course/certified-kubernetes-administrator-with-practice-tests/) - Highly recommended
 - [Killer.sh CKA simulator](https://killer.sh/cka)         ⟹ use code **walidshaari** for **20%** discount  - they update frequently
+- [Kube Academy free How to prepare for the CKA exam training](https://kube.academy/courses/how-to-prepare-for-the-cka-exam)
 - [A Cloud Guru - Certified Kubernetes Administrator (CKA)](https://acloud.guru/overview/certified-kubernetes-administrator)  # k8s version 1.20 - last checked March 2021
 - [LinuxAcademy/ACloudGuru CKA course](https://acloud.guru/learn/7f5137aa-2d26-4b19-8d8c-025b22667e76)  # labs last checked were updated to 1.18
 - [rx-m online CKA course](https://rx-m.com/cka-online-training/)