Add information about how to uninstall Purescript and tools

[mars0i]

It would be useful to have easy to find information about uninstalling Purescript and very closely related tools. I'd recommend putting this information near the end of the Getting Started/guides page. Another option would be to put a link to the information early on that page.

Ideally, uninstall information would include tips or links for uninstalling required or very common tools such spago.

(Why? Because some people--I'm one of them--try out Purescript for a while, and then stop using it, and come back a year or more later. At that point, one can go through an upgrade process, but tools and libraaries may have changed so much that it would be better to clean out whatever is there and reinstall from scratch. After all, Purescript and its tooling are undergoing continual improvement. It may even be that when Purescript was first installed, the method one used was different (maybe I didn't use npm for this purpose, for all I know), and files might not be in the same locations. (Although I suppose that this would present a problem for uninstall documentation.)

/Getting-Started.md