I have started using the following workflow and it's been working out great:
README.mdfile to describe the requirements along with any sample design mockups as an embedded image for a reference.
chart.jsto the repo
From here, I just start building out the visualization I want. To preview things locally, I run:
python -m SimpleHTTPServer 8888
Once I am satisfied with progress, I commit, and then push to the gist. The nice thing about hosting in this format in a GitHub gist is that you can use the bl.ocks.org service to get a nice preview of your visualization.