pull-request template: ask for changelog description

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

.github/PULL_REQUEST_TEMPLATE.md

@@ -19,5 +19,12 @@ Please provide the following information:
 
 **- How to verify it**
 
+**- Description for the changelog**
+<!--
+Write a short (one line) summary that describes the changes in this
+pull request for inclusion in the changelog:
+-->
+
+
 **- A picture of a cute animal (not mandatory but encouraged)**