Make example project app.py executable

The README.doc says to execute ./app.py, but the file is not executable
and does not have a shebang.

Author: 13rac1

examples/flask_sqlalchemy/app.py

@@ -1,3 +1,5 @@
+#!/usr/bin/env python
+
 from flask import Flask
 
 from database import db_session, init_db