Nudge readers towards a more accurate mental model for loop else clauses (Backport from 3.x)

Doc/tutorial/controlflow.rst

@@ -159,6 +159,13 @@ following loop, which searches for prime numbers::
 (Yes, this is the correct code.  Look closely: the ``else`` clause belongs to
 the :keyword:`for` loop, **not** the :keyword:`if` statement.)
 
+When used with a loop, the ``else`` clause has more in common with the
+``else`` clause of a :keyword:`try` statement than it does that of
+:keyword:`if` statements: a :keyword:`try` statement's ``else`` clause runs
+when no exception occurs, and a loop's ``else`` clause runs when no ``break``
+occurs. For more on the :keyword:`try` statement and exceptions, see
+:ref:`tut-handling`.
+
 
 .. _tut-pass: