Fixed fork-and-edit link, added about-us, adjusted the layout a bit and ...

Yepp,  you read right: I added a long missed about-us page ;) Preview as usual at: http://propelorm.jarves.io/about-us.html

Startpage removed the heavy green: http://propelorm.jarves.io/

Please let me know what you think about the about-us page. Its really important to me, that all active developers that work hard on propel are featured there with the right information, of course with Francois and William. Feel free to tell me different website urls for your profile. Order is the same as github shows us in the contribution graph.