Update readme for using on HTML elements
Update readme for using on HTML elements

- Update README to properly denote how to use the library with inline HTML elements
- add `data-` to HTML example attributes
- add `has-tooltip` class to each element with a tooltip, as well as include instructions denoting as such
- taken from https://github.com/sir-dunxalot/ember-tooltips/blob/master/addon/mixins/components/tooltips.js#L127-L184

maxhungry/ember-tooltips,kmiyashiro/ember-tooltips,sir-dunxalot/ember-tooltips,maxhungry/ember-tooltips,zenefits/ember-tooltips,zenefits/ember-tooltips,sir-dunxalot/ember-tooltips,kmiyashiro/ember-tooltips