docs(data): improve DefaultDataServiceConfig root parameter docs (#2075)

Adds more details for the DefaultDataServiceConfig api docs and Entity Dataservice
doc page.  Specifically, added details and examples for providing a remote api to
the DefaultDataServiceConfig root parameter.  Current docs do not include this
information, and it this makes it clear how one would use a remote api, which is
a very common use case.

Closes #2071

modules/data/src/dataservices/default-data-service-config.ts

@@ -5,7 +5,10 @@ import { EntityHttpResourceUrls } from './http-url-generator';
  * such as the `DefaultDataService<T>`.
  */
 export abstract class DefaultDataServiceConfig {
-  /** root path of the web api (default: 'api') */
+  /**
+   * root path of the web api.  may also include protocol, domain, and port
+   * for remote api, e.g.: `'https://api-domain.com:8000/api/v1'` (default: 'api')
+   */
   root?: string;
   /**
    * Known entity HttpResourceUrls.

projects/ngrx.io/content/guide/data/entity-dataservice.md

@@ -101,7 +101,7 @@ The shared configuration values are almost always specific to the application an
 The NgRx Data library defines a `DefaultDataServiceConfig` for 
 conveying shared configuration to an entity collection data service.
 
-The most important configuration property, `root`, returns the _root_ of every web api URL, the parts that come before the entity resource name.
+The most important configuration property, `root`, returns the _root_ of every web api URL, the parts that come before the entity resource name. If you are using a remote API, this value can include the protocol, domain, port, and root path, such as `https://my-api-domain.com:8000/api/v1`.
 
 For a `DefaultDataService<T>`, the default value is `'api'`, which results in URLs such as `api/heroes`.
 
@@ -121,7 +121,7 @@ First, create a custom configuration object of type `DefaultDataServiceConfig` :
 
 ```typescript
 const defaultDataServiceConfig: DefaultDataServiceConfig = {
-  root: 'api',
+  root: 'https://my-api-domain.com:8000/api/v1',
   timeout: 3000, // request timeout
 }
 ```