Please add install instructions

[cdennison]

I did this:

1. Copied index.js to /freeboard/js/jqplot-plugin.js
2. Added to main freeboard index.html
   head.js("js/freeboard_plugins.min.js",
   "js/jqplot-plugin.js",

But I think it would be better it add it to the Gruntfile.js so it can be properly deployed.

[jritsema]

Sure, I will add the instructions to the readme.

The thing with shipping this widget "in the box" with freeboard, is that not everyone might want to use it. I think the idea was to only include the commonly used widgets in the box. Unfortunately, the project creator seems to have abandoned the project, but I did ask what the vision was with the plugins and never got a response. I even submitted this pull request to get my plugins added to the official plugins repo but there's been no response. It would be cool to have some sort of tool that allowed you to easily install plugins from a github repo...