EPiServer CMS 6 and 7 XML documentation files – Visual Studio Intellisense:
EPiServer CMS 6 XML documentation files.
PS. the xml files should be placed in the folder where you referenced dlls are to work!
EPiServer 7 XML files should be included in nuget package:
http://world.episerver.com/Modules/Forum/Pages/Thread.aspx?id=73912&epslanguage=en