Add info for using underscored API endpoints and JSON root objects

Starting in Beta 1 the RESTAdapter tries to send API requests to '/blog-posts' instead of '/blog_posts' as it had done previously.  It also expects the root object of a JSON response to be camelized instead of underscored ('blogPosts' instead of 'blog_posts').  This PR adds info to the TRANSITION document about how to go back to the previous functionality.