Add docs for confirmation endpoint (lynndylanhurley#1365)

docs/usage/README.md

@@ -15,3 +15,4 @@ The following routes are available for use by your client. These routes live rel
 | /password | POST | Use this route to send a password reset confirmation email to users that registered by email. Accepts **`email`** and **`redirect_url`** as params. The user matching the `email` param will be sent instructions on how to reset their password. `redirect_url` is the url to which the user will be redirected after visiting the link contained in the email. |
 | /password | PUT | Use this route to change users' passwords. Requires **`password`** and **`password_confirmation`** as params. This route is only valid for users that registered by email (OAuth2 users will receive an error). It also checks **`current_password`** if **`config.check_current_password_before_update`** is not set `false` (disabled by default). |
 | /password/edit | GET | Verify user by password reset token. This route is the destination URL for password reset confirmation. This route must contain **`reset_password_token`** and **`redirect_url`** params. These values will be set automatically by the confirmation email that is generated by the password reset request. |
+| /confirmation | POST | Re-sends confirmation email. Requires **`email`** and accepts **`redirect_url`** params (this last one can be omitted if you have set `config.default_confirm_success_url` in `config/initializers/devise_token_auth.rb`). |