Fixed GitHub capitalization per #1416

[git-p4: depot-paths = "//vr/steamvr/sdk_release/": change = 6021408]

Author: JoeLudwig

README.md

@@ -8,6 +8,6 @@ and samples. The runtime is under SteamVR in Tools on Steam.
 
 ### Documentation
 
-Documentation for the API is available on the [Github Wiki](https://github.com/ValveSoftware/openvr/wiki/API-Documentation)
+Documentation for the API is available on the [GitHub Wiki](https://github.com/ValveSoftware/openvr/wiki/API-Documentation)
 
 More information on OpenVR and SteamVR can be found on http://steamvr.com