Update extension-activation page

[chrifro]

Problem:
The page is one of the most visited pages, but the bounce rate is really bad with 88% (average 34%), same as the exit rate 69%.

Solution
It might help to move the CTA button further up.

Mockup

Thought: Additionally we can add the example projects from https://www.gitpod.io/#get-started to this page

/cc @gtsiolis