README register link is broken

[cvockrodt]

The register link goes to a page that returns:

{
"error_id":null,
"error_message":"The requested URL was not found on the server.  If you entered the URL manually please check your spelling and try again.",
"error_type":"NotFound",
"error_uri":"http://api.put.io/v2/docs",
"extra":{},
"status":"ERROR",
"status_code":404
}