Fix or suppress HTML warnings in Readme #144

The auto-generated portions of the Readme, namely the contributors section, contains deprecated HTML elements. The resulting warnings were suppressed in a PR (#108), but since the HTML code is regenerated sometimes, we need a more permanent solution.

The first is, as was suggested by @favoyang here to disable HTML warnings for the whole Readme file.

Another is to find out if there is a way to configure the generated HTML code to not contain deprecated elements.