Minikube: Document uninstall procedures

[G-Harmon]

Is this a BUG REPORT or FEATURE REQUEST? (choose one):
Feature Request

There doesn't seem to be documentation on how to properly uninstall minikube. #1043 has a bunch of different sets of commands, depending on what OS and shell you're using.

I ran into the problem of an incompatibility between a year-old version of minikube and current (v30). It took a long time to figure out how to clear out all of minikube's old state, before finding I needed to delete ~/.minikube (linux).

[amruthar]

Need this one for mess-proof uninstallation without the risks of trial and errors!

[blueelvis]

/assign