Add documentation-home layout with hosted/self-hosted links

This will be the page for signposting people to correct set of
documentation depending on whether they want to host it themselves or
self-host.
Add brief explaination of difference between hosted/self-hosted

This will probably need to be expanded in the future, but for now it is
sufficient.
Basic structure for new documentation

This is just the barebones structure, the content isn't complete and
there may be more pages to add or possibly some that can be taken away.
add a quickstart guide for developers
change 'get started' link to new instance page
added final call to action to bottom of the footer
Added footer contact link