Added 'import os' statement

Added 'import os' statement so you can use os.path.join() when defining DATABASE location

docs/tutorial/setup.rst

@@ -14,6 +14,7 @@ load that or import the values from there.
 First we add the imports in `flaskr.py`::
 
     # all the imports
+    import os
     import sqlite3
     from flask import Flask, request, session, g, redirect, url_for, abort, \
          render_template, flash