Fix calvera-test deploy

prepare_charts.js isn't being properly placed into /app/www-content. I did not realize this when testing the local Docker build because I was unintentionally bypassing the nginx proxy. I'm going to make the following changes:

1. Ensure that prepare_charts.js is properly loaded into /app/www-content.
2. Update the Docker instructions in our README to ensure that future newbies don't fall into this same trap when testing.