add documentation for umbEmptyState

src/Umbraco.Web.UI.Client/src/common/directives/components/umbemptystate.directive.js

@@ -1,3 +1,29 @@
+/**
+@ngdoc directive
+@name umbraco.directives.directive:umbEmptyState
+@restrict E
+@scope
+
+@description
+Use this directive to show an empty state message.
+
+<h3>Markup example</h3>
+<pre>
+    <div ng-controller="My.Controller as vm">
+
+        <umb-empty-state
+            ng-if="!vm.items"
+            position="center">
+            // Empty state content
+        </umb-empty-state>
+
+    </div>
+</pre>
+
+@param {string=} size Set the size of the text ("small", "large").
+@param {string=} position Set the position of the text ("center").
+**/
+
 (function() {
    'use strict';