Typo corrections (#89)

In this doc mentioned path for `https://example.com/admin/role` returning 404, the correct path is `https://example.com/admin/roles`. Also, button name is `New Role` not `Add Role`.

These two typos corrected.

A big thanks for this contribution.

Author: AjithLalps

docs/roles.md

@@ -9,9 +9,9 @@ php artisan multiauth:role rolename
 ```
 
 2. Using Interface
-   Just go to `https://example.com/admin/role`
+   Just go to `https://example.com/admin/roles`
 
-Now you can click on `Add Role` button to create new role.
+Now you can click on `New Role` button to create new role.
 
 ::: tip To Edit/Delete
 Edit or Delete Role can also be done with same interface