add a code of conduct (#204)

A modified version of Ember's general code of conduct.

Co-authored-by: Casey Watts <[email protected]>

Author: 2 people

CODE_OF_CONDUCT.md

@@ -0,0 +1,6 @@
+# Code Of Conduct
+
+The `ember-sortable` core team and and the broader `Ember` community are committed to everyone having a safe and inclusive experience.
+
+- Our **Community Guidelines / Code of Conduct** can be found at [emberjs.com/guidelines](https://emberjs.com/guidelines/)
+- A history of updates to this page is located at [https://github.com/emberjs/website/commits/master/source/guidelines.html.erb](https://github.com/emberjs/website/commits/master/source/guidelines.html.erb)