Add a note for developers

skel/etc/zope.conf.in

@@ -8,6 +8,17 @@
 # you add it to a line that does not begin with '#'.  Note that comments
 # are only allowed at the beginning of a line: you may not add comments
 # after directive text on the same line.
+#
+# Note for Developers
+# ===================
+#
+# This file is *not* auto-generated. If you create a new directive you
+# very likely want to include an example of how to use the new
+# directive in this file.
+#
+# You shouldn't modify 'zope.conf.in' to change
+# configuration. Instead, you should make a copy into 'zope.conf' and
+# modify that to avoid checking in changes to this file by mistake.
 
 # ZConfig "defines" used for later textual substitution