use rich markup for PEP reference (pythonGH-7939)

bbmokhtari · benjaminp · commit df748c20dabc · 2018-06-26T20:57:39.000-07:00
it's better to refer to PEP with `pep` role in reStructuredText. It also links to the PEP page.
diff --git a/Doc/tutorial/modules.rst b/Doc/tutorial/modules.rst
@@ -249,7 +249,7 @@ Some tips for experts:
   directory.
 
 * There is more detail on this process, including a flow chart of the
-  decisions, in PEP 3147.
+  decisions, in :pep:`3147`.
 
 
 .. _tut-standardmodules:
