Documentation files that you downloaded from GitHub are in markdown format. Generally speaking you can open the .md file with any text editor. If you want a more user-friendly appearance you may use a special tool like MarkdownPad
(it's free) or other of your choice.
On a side note, I am glad to inform you that docs.kendoui.com is available again. Once again, please accept my apology for the inconvenience caused.
the Telerik team
Join us on our journey to create the world's most complete HTML 5 UI Framework - download Kendo UI