Add missing deprecation comments (#1482)

Author: IvanGoncharov

src/utilities/extendSchema.js

@@ -68,6 +68,7 @@ type Options = {|
    * Descriptions are defined as preceding string literals, however an older
    * experimental version of the SDL supported preceding comments as
    * descriptions. Set to true to enable this deprecated behavior.
+   * This option is provided to ease adoption and will be removed in v16.
    *
    * Default: false
    */

src/utilities/schemaPrinter.js

@@ -38,7 +38,17 @@ import {
 } from '../type/directives';
 import { isIntrospectionType } from '../type/introspection';
 
-type Options = {| commentDescriptions?: boolean |};
+type Options = {|
+  /**
+   * Descriptions are defined as preceding string literals, however an older
+   * experimental version of the SDL supported preceding comments as
+   * descriptions. Set to true to enable this deprecated behavior.
+   * This option is provided to ease adoption and will be removed in v16.
+   *
+   * Default: false
+   */
+  commentDescriptions?: boolean,
+|};
 
 /**
  * Accepts options as a second argument: