Enable including extra content on homepage

Include (extra) content specified in the /??/index.html file
at the top of the generated homepage. Currently only meant
for an "unmaintained translation" message.

Author: stomar

_layouts/homepage.html

@@ -11,6 +11,8 @@
 
 ---
 
+{{ content }}
+
 {% assign number_of_excerpts = 4 %}
 {% assign number_of_other    = 3 %}{% comment %} number of links per column {% endcomment %}