Add documentation to main js file

addon/components/form-field.js

@@ -3,6 +3,17 @@ import { isPresent } from '@ember/utils';
 import { computed } from '@ember/object';
 import Component from '@ember/component';
 
+//
+// A generic wrapper around a form element (input, select, radios)
+//
+// By providing this component with an attribute name on a model, this component will auto-detect any validation errors (from DS.Errors)
+// on the specified attribute, and apply appropriate error classes and error messages to the field.
+//
+// This component also support custom errors that is not part of the model (client-side validations, for example).
+// Although comprehensive client-side validation libraries are available, we do not currently need the full capability of those libraries and a simple custom error string will do.
+//
+// This component is a modified and simplified version of https://alexspeller.com/server-side-validations-with-ember-data-and-ds-errors/
+//
 export default Component.extend({
   classNameBindings: [':form-group', 'hasError:has-error'],