Update README.md

Fix link to working examples in boilerplate-swig instead of assemble-swig-examples. Managed to track this down from [Jon's SO answer](http://stackoverflow.com/questions/18015532/using-template-inheritance-with-assemble/18021580#18021580).

Needs to be updated on all Related projects:
<ul>
<li>
<a href="https://github.com/jonschlinkert/sublime-swig">sublime-swig</a> syntax highlight for Swig Templates, in Sublime Text.</li>
<li><a href="https://github.com/jonschlinkert/sublime-monokai-extended">sublime-monokai-extended</a></li>
<li><a href="https://github.com/jonschlinkert/sublime-markdown-extended">sublime-markdown-extended</a></li>
<li>
<a href="http://github.com/assemble">assemble</a> (see the <a href="http://assemble.io">live docs</a>)</li>
<li><a href="http://github.com/assemble/assemble-swig">assemble-swig</a></li>
<li><a href="http://github.com/assemble/boilerplate-swig">boilerplate-swig</a></li>
</ul>