(docs) add workerpath sample to readme

This update adds instructions for using the new `workerPath` property to circumvent problems that `ace` encounters when using bundled, concatenated, minified, and uglified sources. 

## Support for concatenated bundles

Trying to use ace with concatenated javascript files usually fails because it changes the physical location of the `workerPath`. If you
need to work with bundled or minified versions of ace, you can specify the original location of the `workerPath` on disk (_not the bundled file_).

This should be the folder on disk where `ace.js` resides.

```html
<div ui-ace="{
  workerPath: '/path/to/ace/folder'
}"></div>
```