Improve "marketing" page

[balinterdi]

Now that the add-on uses ember-cli-addon-docs, the barrier to come up with a decent marketing page and deploy it is really low.

My first idea is to have ratings for different skills for a few chess players (Carlsen, Nakamura, myself :) ) in a nice table form. Rated properties could be "standard", "rapid", "blitz", "tactics", "positional play", "endgame", etc.