Extend information on landing page to detail what feedback we're currently looking for

This wording is based on the discussed text with a minor couple of alterations from proof reading as I was inserting it in the page.

I've also done a minor change so that both sections are hidden on page load, and only the required section is shown. This should stop the flickering whilst the js loads.

We could probably prettify it more, but I suggest we get the basic text landed and then sort out extra styles later.

Suggest review from @dmose