Explicitly state that PEP 488 doesn't influence import performance

pep-0488.txt

@@ -108,6 +108,15 @@ passed to the interpreter then instead of
 ``importlib.cpython-35.pyo`` the file name would be
 ``importlib.cpython-35.opt-2.pyc``.
 
+It should be noted that this change in no way affects the performance
+of import. Since the import system looks for a single bytecode file
+based on the optimization level of the interpreter already and
+generates a new bytecode file if it doesn't exist, the introduction
+of potentially more bytecode files in the ``__pycache__`` directory
+has no effect. The interpreter will continue to look for only a
+single bytecode file based on the optimization level and thus no
+increase in stat calls will occur.
+
 
 Implementation
 ==============