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)