Better README

[osxi]

The README is very lacking.

I think we should add some instructions for end developers and some notes for those interested in maintaining the addon.

Also, when the README is mature, https://emberobserver.com/addons/ember-date-range-picker will indicate that this project has grown past the WIP state.

[knittingdev]

Here are a list of things I think we can document:

• [ ] Usage of the different pickers
• [ ] The options available for each picker
• [ ] How to Start the dummy application
• [ ] How to Contribute
• [ ] Code of Conduct (I recommend we use http://contributor-covenant.org/)
• [ ] Goals of the project
• [ ] Versions used

[osxi]

Sounds good to me!

The only thing I can think of that might be important is:

• Mentioning that the default blueprint needs to be run if you add the package to package.json manually or use npm install --save[-dev]
• Mentioning any Ember version incompatibilities (haven't researched this at all with our addon)