Docs/CSS fix: Allow viewport expand to user's preference

Docs/CSS fix: Aallow viewport expand to user's preference

> Note: Closes https://github.com/dotcloud/docker/issues/5277

This commit removes the "max-width" property of DOM "containers";
Thus letting the viewport to expand to fill the available space.

This commit aims to bring pleasure to Docker docs' readers' eyes,
And to make them happy by letting them profit more from their large
monitors. (or use more efficiently their smaller ones).

Docker-DCO-1.1-Signed-off-by: O.S. Tezer <ostezer@gmail.com> (github: ostezer)