Added import of SQLite3

exercises/3-create-a-db-from-csv/README.md

@@ -14,6 +14,7 @@ Take a look here at Python's sqlite driver [documentation](https://docs.python.o
 
 You need to establish a database and a cursor object.
 ```py
+import sqlite3
 conn = sqlite3.connect('mydb.db')
 c = conn.cursor()
 ```