Added warning message for online usage

## Online warning
What about adding a warning somewhere on the page (I'm not sure if this is the best place though, I'm open to suggestions) for using the generator online?

It's definitely a little on the paranoid side, so I don't know if you'll want to pull this in but let me know what you think.

Here's what the warning currently looks like:
![Warning Screenshot](http://i.imgur.com/4PhsZvU.png)