Clarify preferred way to break at a binary operator.

pep-0008.txt

@@ -87,7 +87,8 @@ Code lay-out
     continuation inside parentheses, brackets and braces.  If necessary, you
     can add an extra pair of parentheses around an expression, but sometimes
     using a backslash looks better.  Make sure to indent the continued line
-    appropriately.  Some examples:
+    appropriately.  The preferred place to break around a binary operator is
+    *after* the operator, not before it.  Some examples:
 
     class Rectangle(Blob):
 
@@ -99,7 +100,8 @@ Code lay-out
                 raise ValueError("sorry, you lose")
             if width == 0 and height == 0 and (color == 'red' or
                                                emphasis is None):
-                raise ValueError("I don't think so")
+                raise ValueError("I don't think so -- values are %s, %s" %
+                                 (width, height))
             Blob.__init__(self, width, height,
                           color, emphasis, highlight)