Update CONTRIBUTING.md
Update CONTRIBUTING.md

Fix header markdown
jamespearce2006/CefSharp,Livit/CefSharp,jamespearce2006/CefSharp,jamespearce2006/CefSharp,jamespearce2006/CefSharp,Livit/CefSharp,Livit/CefSharp,Livit/CefSharp,jamespearce2006/CefSharp