Update README

[kybishop]

One currently has to read the source to see how ember-popper works... we should really fix this.

[pzuraq]

ec-addon-docs? 😄

[kybishop]

Super down. I'll give it a go soon

[stfcodes]

I'd really like to get some documentation as well. Browsing code isn't that hard, yet after a being away from ember for a while + not being familiar with these libraries in the first place (tether poper etc), understanding the whole context is pretty daunting.

ember-cli-addon-docs is a great fit, and even if it's easier to add than actually creating interactive documentation from scratch, it's still a bigger effort compared to updating the readme itself.

Baby steps 😄.