Fixed #22007 -- Fixed cbv docs - make imports consistent

Thanks to trac user kinjal.dixit for the report.

docs/internals/contributing/writing-code/coding-style.txt

@@ -30,6 +30,14 @@ Python style
 * Use ``InitialCaps`` for class names (or for factory functions that
   return classes).
 
+* Use convenience imports whenever available. For example, do this::
+
+      from django.views.generic import View
+
+  Don't do this::
+
+      from django.views.generic.base import View
+
 * In docstrings, use "action words" such as::
 
       def foo():