Update documentation links on README
Update documentation links on README

mnapoli/Slim,designermonkey/Slim,iinux/Slim,foxyantho/Slim,RealSelf/Slim,iinux/Slim,JoeBengalen/Slim,jaapverloop/Slim,samsonasik/Slim,iinux/Slim,dopesong/Slim,feryardiant/slim,slimphp/Slim,Sam-Burns/Slim,AndrewCarterUK/Slim,juliangut/Slim,akrabat/Slim