Add License file

Hi,

I'm in the process of adding this project as an RPM package in Fedora. One of the recommendations when adding a package to Fedora is to check if the upstream project (you!) has a copy of the text of the license. If one doesn't exist, we ask if it can be included.

Of course, it's not a requirement of all licenses to have a full copy of the license text in projects that it covers, and the LGPLv2.1+ is one of those licenses that doesn't require it, but it sure helps to make things clearer without having to look into the source code files. :) A pull request seems the easiest way for everyone involved to propose things like this.

If you are interested in following the process of inclusion into Fedora, you can do so by following this bugzilla issue: https://bugzilla.redhat.com/show_bug.cgi?id=989014
If you have any questions about it, please let me know. Likewise, if you get reports of users encountering problems while using the Fedora packaged version of this, please let me know about those too!

Regards and thanks for creating this,
Gerard.