Improve the landing page for aka.ms/qdk

[billti]

We use this shortlink in a number of places, including introductory videos. This currently goes to a page on how to install the QDK. For those completely new to the QDK, it might be of more value if it landed on an overview page to educate them on what it is, why you might want it, features overview, etc.

[billti]

Let's discuss with the team on what we might want to do here. No action needed until we have a plan.