(docs) update docs/start/_index.md`

minikube is not a cask on brew

- update doc wording to reflect the change
- update image reflecting this

site/content/en/docs/start/_index.md

@@ -81,10 +81,10 @@ If the [Brew Package Manager](https://brew.sh/) installed:
 brew install minikube
 ```
 
-If `which minikube` fails after installation via brew, you may have to remove the minikube cask and link the binary:
+If `which minikube` fails after installation via brew, you may have to remove the old minikube links and link the newly installed binary:
 
 ```shell
-brew cask remove minikube
+brew unlink minikube
 brew link minikube
 ```