Add jQuery dependency to README

[Schroedingberg]

The templates require jQuery to work. Without it you'll get a Uncaught ReferenceError: $ is not defined.

This should be mentioned in the dependencies, since some people might not want to add jQuery to their project.

Also, it looks to me like the things that jQuery is used for here are not extremely complex, so it might be a nice future improvement to change this to vanila JS to keep dependencies minimal.
If you are interested in that, I can try and do that after I am done with my current project.