[netinstall] Point documentation towards netinstall README.md

src/modules/netinstall/netinstall.conf

@@ -4,6 +4,13 @@
 #   groupsUrl: http://example.org/netinstall.php
 # or it can be a locally installed file:
 #   groupsUrl: file:///usr/share/calamares/netinstall.yaml
+#
+# Note that the contents of the groups file is the **inmportant**
+# part of the configuration of this module. It specifies what
+# the user may select and what commands are to be run.
+#
+# The format of the groups file is documented in `README.md`.
+#
 # groupsUrl: file:///usr/share/calamares/netinstall.yaml
 
 # If the installation can proceed without netinstall (e.g. the Live CD

src/modules/netinstall/netinstall.yaml

@@ -1,3 +1,7 @@
+# Example configuration with groups and packages, taken from Chakra Linux.
+#
+# This example is rather limited. See `README.md` for full documentation
+# on the configuration format.
 - name: "Default"
   description: "Default group"
   hidden: true