Document changes to hostname_prefix field of site.conf

docs/releases/v2015.1.rst

+Gluon 2015.1 (in development)
+=============================
+
+Added (and removed) hardware support
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+
+New features
+~~~~~~~~~~~~
+
+
+Bugfixes
+~~~~~~~~
+
+
+Site changes
+~~~~~~~~~~~~
+* ``site.conf``
+
+  - ``hostname_prefix`` is now optional, and is concatenated directly with the
+    generated node ID, in particular no hyphen is inserted anymore. If you want
+    to keep the old behaviour, you have to append the hyphen to the
+    ``hostname_prefix`` field of your ``site.conf``.
+
+Internals
+~~~~~~~~~
+
+
+Known Issues
+~~~~~~~~~~~~

docs/site-example/site.conf

@@ -6,8 +6,8 @@
 -- This configuration will not work as it. You're required to make
 -- community specific changes to it!
 {
-  -- Used for generated hostnames, e.g. freifunk-abcdef123456.
-  hostname_prefix = 'freifunk',
+  -- Used for generated hostnames, e.g. freifunk-abcdef123456. (optional)
+  -- hostname_prefix = 'freifunk-',
 
   -- Name of the community.
   site_name = 'Freifunk Entenhausen',