Update getting started instructions to match latest version

Hi, I've been playing with your citeproc-java library, and been trying to just do the "getting started" instructions here, but have run into some problems.

I've gotten it to work up until the very last step, "makeBibliography", but I had to change a lot minor aspects of the code -- so I updated your GH page, and here are the changes.

Now, for the final step, I am getting a cryptic error
    Caught exception: java.lang.IllegalArgumentException: Could not make bibliography
and I've tried lots of different things, and can't get it to work.  I've traced it through your java code, and see that the error is coming from the citeproc-js runner.

The strange thing is that the CSLTest::bibliography test works, when I run it from gradlew, which seems to do basically the same thing.  I guess there must a problem with my classpath.  Right now it has the following in it:
* .
* \<github clone>/michel-kraemer/citeproc-java/build/libs/citeproc-java-0.6.jar
* \<downloaded>/commons-lang3-3.2.1/commons-lang3-3.2.1.jar
* \<downloaded>/junit-4.11.jar
* \<csl directory>

Any ideas what could be wrong, off the top of your head?