test: add test links

Author: adamdbradley

src/test/fixtures/definitions.ts

@@ -5,6 +5,8 @@
  * the `HapticsPlugin` interface. All the API data below
  * is generated from comments from its methods, interfaces
  * and enums.
+ *
+ * Take a look at the test [HapticsPlugin interface source file](https://github.com/ionic-team/capacitor-docgen/blob/master/src/test/fixtures/definitions.ts).
  */
 export interface HapticsPlugin {
   /**