docs(ajax): added ajax and webSocket docs back to the list (#3984)

docs_app/tools/transforms/angular-api-package/index.js

@@ -68,7 +68,10 @@ module.exports = new Package('angular-api', [basePackage, typeScriptPackage])
  // NOTE: This list should be in sync with tools/public_api_guard/BUILD.bazel
  readTypeScriptModules.sourceFiles = [
  'index.ts',
- 'operators/index.ts'
+ 'operators/index.ts',
+ 'ajax/index.ts',
+ 'webSocket/index.ts',
+ 'testing/index.ts'
  ];
 
  // API Examples

src/internal/observable/dom/ajax.ts

@@ -1,3 +1,19 @@
 import { AjaxObservable, AjaxCreationMethod } from './AjaxObservable';
-
+/**
+ * There is an ajax operator on the Rx object.
+ *
+ * It creates an observable for an Ajax request with either a request object with
+ * url, headers, etc or a string for a URL.
+ *
+ * ## Using ajax.getJSON() to fetch data from API.
+ * ```javascript
+ * import { ajax } from 'rxjs/ajax';
+ * import { map, catchError } from 'rxjs/operators';
+ *
+ * const obs$ = ajax.getJSON(`https://api.github.com/users?per_page=5`).pipe(
+ * map(userResponse => console.log('users: ', userResponse)),
+ * catchError(error => console.log('error: ', error))
+ * ));
+ * ```
+ */
 export const ajax: AjaxCreationMethod = AjaxObservable.create;