Documentation need for the demo

Hi, just some suggestion to add more details about this script in the README:

sonic-annotator -d vamp:bbc-vamp-plugins:bbc-rhythm:tempo audio.wav -w csv --csv-stdout

Eg:

Where is the output file (same folder, or set new folder with --csv-basedir newfolder), and what is the correct output of this script, and what is the correct file content of that feature.

Thanks
