Add notes for porting issues related to pickles.
diff --git a/Doc/whatsnew/3.1.rst b/Doc/whatsnew/3.1.rst
index 290cd5c..30b3f24 100644
--- a/Doc/whatsnew/3.1.rst
+++ b/Doc/whatsnew/3.1.rst
@@ -541,3 +541,8 @@
Got:
2.718281828459045
**********************************************************************
+
+* The automatic name remapping in the pickle module for protocol 2 or lower can
+ make Python 3.1 pickles unreadable in Python 3.0. One solution is to use
+ protocol 3. Another solution is to set the *fix_imports* option to **False**.
+ See the discussion above for more details.