doc: internal_net_only in meta-fields, python-netaddr in README

README.org

@@ -4,6 +4,7 @@
   - jinja
   - python2
   - python-pdfminer (for pdf2txt, used in metadata reading)
+  - python-netaddr
 
 * Setup
 ** Base config

doc/meta-fields.org

@@ -28,6 +28,8 @@
     of tuples (studiengang, semester, wahlpflicht) :: (String, String, String),
     where each values is imported as-is from univis.
   - department: department this lecture is provided by
+  - internal_net_only: this evaluation can only be accessed from the
+    internal network (set in config)
 
   Optionally (for to-be-moderated entries):