Interlinked design docs better

docs/design.rst

@@ -1,3 +1,5 @@
+.. _design:
+
 Design Decisions in Flask
 =========================
 
@@ -109,6 +111,10 @@ A template abstraction layer that would not take the unique features of
 the template engines away is a science on its own and a too large
 undertaking for a microframework like Flask.
 
+Furthermore extensions can then easily depend on one template language
+being present.  You can easily use your own templating language, but an
+extension could still depend on Jinja itself.
+
 
 Micro with Dependencies
 -----------------------

docs/foreword.rst

@@ -44,6 +44,9 @@ However Flask is not much code and built in a very solid foundation and
 with that very easy to adapt for large applications.  If you are
 interested in that, check out the :ref:`becomingbig` chapter.
 
+If you are curious about the Flask design principles, head over to the
+section about :ref:`design`.
+
 A Framework and an Example
 --------------------------