Settings -> System Settings -> Addons and enable "Unknown Sources"
Then follow the instructions here:http://www.urepo.org/install.php
Then go into (From the First screen of Kodi):
Addons -> Download -> .. <- i.e. go up one directory
Then "Install From repository" -> uRepo -> "Program Addons" -> Sonos
The Kodi team have made it very awkward for everyone to install addons that they can not impose influence over ... they've not really done anyone any favours there!
Hope this helps