Improve whitespace docs to reflect reality.

See also:
https://groups.google.com/d/msg/pocoo-libs/6DylMqq1voI/GXTbZJ1Tr-sJ

docs/templates.rst

@@ -152,10 +152,11 @@ yourself::
 Whitespace Control
 ------------------
 
-In the default configuration whitespace is not further modified by the
-template engine, so each whitespace (spaces, tabs, newlines etc.) is returned
-unchanged.  If the application configures Jinja to `trim_blocks` the first
-newline after a a template tag is removed automatically (like in PHP).
+In the default configuration, a single trailing newline is stripped if
+present, and whitespace is not further modified by the template engine. Each
+whitespace (spaces, tabs, newlines etc.) is returned unchanged.  If the
+application configures Jinja to `trim_blocks` the first newline after a a
+template tag is removed automatically (like in PHP).
 
 But you can also strip whitespace in templates by hand.  If you put an minus
 sign (``-``) to the start or end of an block (for example a for tag), a