Add (minimal) discussion about restartability.

pep-0234.txt

@@ -168,6 +168,10 @@ Python API Specification
       this may require an additional state bit for some iterator
       implementations (e.g. function-wrapping iterators).
 
+    - Some folks have requested the ability to restart an iterator.  I
+      believe this should be dealt with by calling iter() on a
+      sequence repeatedly, not by the iterator protocol itself.
+
     - It was originally proposed that rather than having a next()
       method, an iterator object should simply be callable.  This was
       rejected in favor of an explicit next() method.  The reason is