List get-started content under guides

[simon04]

Related: #743, #749.

Supersedes #773 (wrong source branch).

[bebraw]

It might be a good idea to write redirects for the pages. The syntax is like this:

    redirects: {
      'get-started': '/guides/get-started'
    }

That should go below the path definition next to path() etc. Consider building only that portion of the site when testing the build (comment out everything else).

[simon04]

I added the redirects, and extracted the syntax from here.