Added usage example

Author: jeongheeyeun

docs/index.html

@@ -60,7 +60,12 @@ <h3 class="section-title">How to use</h3>
         {% highlight css %}font-family: 'open-arrow', Helvetica, sans-serif;
 {% endhighlight %}
     </li>
-
+    <li>
+      Use it like this:
+      {% highlight html %} &#x2192 Use it like this &#x2190
+{% endhighlight %}
+      <div class="preview">&#x2192 Use it like this &#x2190</div>
+    </li>
   </ol>
 </section>
 <script type="text/javascript">

docs/stylesheets/style.scss

@@ -183,3 +183,10 @@ code.unicode {
   border: none;
 }
 
+.preview {
+  margin: 1em 0 0;
+  padding: 1em 1.5em;
+  border: 2px dotted $oc-gray-7;
+  border-radius: 4px;
+}
+