Fix quickstart example

If someone run the quickstart sample equal to the example, will be fail, because render_template is not imported.

Author: eamanu

README.md

@@ -5,7 +5,7 @@ PyMongo support for Flask applications
 ## Quickstart
 
 ```python
-from flask import Flask
+from flask import Flask, render_template
 from flask_pymongo import PyMongo
 
 app = Flask(__name__)