Update backbone-javascript-client.md

Please include the information about how to create the backbone api function for custom endpoints. It is not found anywhere in this documentation and took me a few days to figure this out.

Author: Oblivious1

using-the-rest-api/backbone-javascript-client.md

@@ -241,7 +241,7 @@ post.getRevisions().done( function( revisions ){
 });
 ```
 
-If you add custom endpoints to the API they will also become available as models/collections. For example, you will get new models and collections when you [add REST API support to your custom post type](https://developer.wordpress.org/rest-api/extending-the-rest-api/adding-rest-api-support-for-custom-content-types/). Note: Because the schema is stored in the user's session cache to avoid re-fetching, you may need to open a new tab to get a new read of the Schema.
+If you add custom endpoints to the API they will also become available as models/collections. For example, you will get new models and collections when you [add REST API support to your custom post type](https://developer.wordpress.org/rest-api/extending-the-rest-api/adding-rest-api-support-for-custom-content-types/). To access custom endpoints created, use the item's JSON endpoint name as CamelCase; for example if the item is found at the JSON path of /wp-json/wp/v2/my-custom-post, it can be accessed via the api at wp.api.collections.MyCustomPost.  Note: Because the schema is stored in the user's session cache to avoid re-fetching, you may need to open a new tab to get a new read of the Schema.
 
 ```js
 // Extend wp.api.models.Post and wp.api.collections.Posts to load a custom post type