Rename links to Getting Started page to Setup page 

I wonder why the English isn't consistent here.  In several places, the page is called "Getting Started".  The file is "Getting Started".  Yet the text here is "Jamulus setup page".  @gilgongo any ideas?

_Originally posted by @pljones in https://github.com/jamulussoftware/jamuluswebsite/pull/811#discussion_r962366493_