Adding link to the promises being used

Author: fresheneesz

README.md

@@ -2,7 +2,9 @@ stacktrace.js
 ===============
 [![Build Status](https://travis-ci.org/stacktracejs/stacktrace.js.svg?branch=master)](https://travis-ci.org/stacktracejs/stacktrace.js) [![Coverage Status](https://img.shields.io/coveralls/stacktracejs/stacktrace.js.svg)](https://coveralls.io/r/stacktracejs/stacktrace.js?branch=master) [![Code Climate](https://codeclimate.com/github/stacktracejs/stacktrace.js/badges/gpa.svg)](https://codeclimate.com/github/stacktracejs/stacktrace.js)
 
-A JavaScript tool that allows you to debug your JavaScript by giving you a [stack trace](http://en.wikipedia.org/wiki/Stack_trace) of function calls leading to an error (or any condition you specify)
+A JavaScript tool that allows you to debug your JavaScript by giving you a [stack trace](http://en.wikipedia.org/wiki/Stack_trace) of function calls leading to an error (or any condition you specify).
+
+The promises referenced below are [ES6-Promises](https://github.com/jakearchibald/es6-promise).
 
 ## Usage
 ```js