Update install-kubectl.md to include instructions for kubectl auto-completion in oh-my-zsh (#4370)

* Update install-kubectl.md

* Move Oh-My-Zsh and edit

* add "the"

docs/tasks/tools/install-kubectl.md

@@ -187,6 +187,13 @@ kubectl completion bash > $(brew --prefix)/etc/bash_completion.d/kubectl
 
 The Homebrew project is independent from kubernetes, so the bash-completion packages are not guaranteed to work.
 
+### Using Oh-My-Zsh
+When using [Oh-My-Zsh](http://ohmyz.sh/), edit the ~/.zshrc file and update the `plugins=` line to include the kubectl plugin.
+
+```shell
+plugins=(git zsh-completions kubectl)
+```
+
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