Fix grammar of landing page text

[hburn7]

The landing page text doesn't feel that great. We'll have to revisit what we want to say before we go live.

[cytusine0]

I started a draft of this a few weeks back in this Google doc, but changes still need to be made and what exactly we put on the page depends on what features we have at release.

[hburn7]

Some changes have been made, but needs QA feedback