Add a new "Docs" link to the top menu pointing to the wiki

[OndroMih]

Our Wiki is currently the most updated source of knowledge and documentation about the project. It's probably the best way to start learning about MicroProfile. It should be linked from the front page, for example as a new "Docs" or "About" link.

The Wiki is now linked in the Eclipse project page in Project links in the sidebar, but it's easy to miss. The project page is linked from the microprofile.io page with the "See the code" link, so people wouldn't expect documentation there.