Update docs

Author: shayneo

README.md

@@ -45,6 +45,12 @@ Most of the props line up with Fuse.js `options` with the defaults set to match
     <th>Type</th>
     <th>Default values</th>
   </tr>
+  <tr>
+    <td>placeholder</td>
+    <td>placeholder text for the input</td>
+    <td>String</td>
+    <td>""</td>
+  </tr>
   <tr>
     <td>eventName</td>
     <td>give a name to the event emitted when the search results are updated</td>