Update README.rst

Fixed typo

Author: sornars

README.rst

@@ -64,7 +64,7 @@ an existing connection by username@database
     ======================
     Poet       733
 
-If no connect string is supplied, ``5sql`` will provide a list of existing connections;
+If no connect string is supplied, ``%sql`` will provide a list of existing connections;
 however, if no connections have yet been made and the environment variable ``DATABASE_URL``
 is available, that will be used.