message: Clarify behavior of Add Owner.
diff: @@ -484,8 +484,12 @@ A successful response includes the JSON object:
  - Method: PUT
  - Authorization: Included
  -A PUT request will add a new owner to a crate. The request should include the
  -following JSON object:
  +A PUT request will send a request to the registry to add a new owner to a
  +crate. It is up to the registry how to handle the request. For example,
  +[crates.io] sends an invite to the user that they must accept before being
  +added.
  +
  +The request should include the following JSON object:
  ```javascript
  {
  