README should link to Codepen Pen

[ctsstc]

The read me should link to the codepen pen page where you can read more about it and install the bookmarklet.

In the future the readme should have more information in it or replicate what's on the codepen page. It may be possible to no longer rely on the codepen page. It would be even greater if the readme could be built out or a post-commit-hook could build it out.