add license file

Your `package.json` indicates this node module is available under the BSD license.

The thingy most people call the BSD license states:
```
    * Redistributions of source code must retain the above copyright
      notice, this list of conditions and the following disclaimer.
    * Redistributions in binary form must reproduce the above copyright
      notice, this list of conditions and the following disclaimer in the
      documentation and/or other materials provided with the distribution.
```
In order to comply with the terms we believe you wish your code to be used under, we are including the copy of the LICENSE file included with this pull request with the Fedora package for this module.

If our assumption is incorrect, please let us know. If you'd like to make it easier for others to reuse your work in the future, please merge this pull request.

Thanks!