Add link to active fork to readme

Since there hasn't been an update to the repo for a long time, [jindw#259](this project has been forked).
I hope this PR helps increase the visibility (besides making it very easy for the original maintainer to make it a statement, e.g. before archiving the repo.)

readme.md

@@ -1,5 +1,7 @@
 # XMLDOM [![Build Status](https://secure.travis-ci.org/bigeasy/xmldom.png?branch=master)](http://travis-ci.org/bigeasy/xmldom) [![Coverage Status](https://coveralls.io/repos/bigeasy/xmldom/badge.png?branch=master)](https://coveralls.io/r/bigeasy/xmldom) [![NPM version](https://badge.fury.io/js/xmldom.png)](http://badge.fury.io/js/xmldom)
 
+***This project has been forked and is now maintained at https://github.com/xmldom/xmldom***
+
 A JavaScript implementation of W3C DOM for Node.js, Rhino and the browser. Fully
 compatible with `W3C DOM level2`; and some compatible with `level3`. Supports
 `DOMParser` and `XMLSerializer` interface such as in browser.