step-75: added link to external repository.

diff --git a/examples/step-75/doc/results.dox b/examples/step-75/doc/results.dox
index 677282951b9879f5d27d957d0e24417b165c8320..b8b2905811becb8be940a26ffb4bfa1e7ca3454b 100644 (file)
--- a/examples/step-75/doc/results.dox
+++ b/examples/step-75/doc/results.dox
@@ -118,6 +118,14 @@ to degree six:
 <a name="extensions"></a>
 <h3>Possibilities for extensions</h3>
 
+This tutorial shows only one particular way how to use parallel
+hp-adaptive finite element methods. In the following paragraphs, you
+will get to know which alternatives are possible. Most of these
+extensions are already part of https://github.com/marcfehling/hpbox/,
+which provides you with implementation examples that you can play
+around with.
+
+
 <h4>Different hp-decision strategies</h4>
 
 The deal.II library offers multiple strategies to decide which type of