Clarify section about source code encoding.

Doc/tutorial/interpreter.rst

@@ -185,8 +185,8 @@ encodings can be found in the Python Library Reference, in the section on
 
 For example, to write Unicode literals including the Euro currency symbol, the
 ISO-8859-15 encoding can be used, with the Euro symbol having the ordinal value
-164.  This script will print the value 8364 (the Unicode codepoint corresponding
-to the Euro symbol) and then exit::
+164.  This script, when saved in the ISO-8859-15 encoding, will print the value
+8364 (the Unicode codepoint corresponding to the Euro symbol) and then exit::
 
    # -*- coding: iso-8859-15 -*-