[netinstall] Massage the documentation a little

src/modules/netinstall/netinstall.conf

@@ -178,10 +178,11 @@ label:
 #    the group's packages are installed. It will run after **each** package in
 #    the group is installed.
 #
-# If you set both *hidden* and *selected* for a group, you are basically
+# If you set both *hidden* and *selected* for a top-level group, you are
 # creating a "default" group of packages which will always be installed
-# in the user's system. Setting *hidden* to true without *selected*, or with
+# in the user's system. Hidden selected subgroups are installed if their
-# *selected* set to false, is kind of pointless.
+# parent is selected. Setting *hidden* to true without *selected*, or with
+# *selected* set to false, is kind of pointless and will generate a warning.
 #
 # The *pre-install* and *post-install* commands are **not** passed to
 # a shell; see the **packages** module configuration (i.e. `packages.conf`)
@@ -291,11 +292,13 @@ groups:
     #
     # The name of the internal subgroup doesn't matter -- it is hidden
     # from the user -- so we can give them all bogus names and
-    # descriptions, even the same name. Here, we use "bogus".
+    # descriptions, even the same name. Here, we use "Bogus". You
+    # can re-use the subgroup name, it doesn't really matter.
     #
     # Each internal subgroup is set to *hidden*, so it does not show up
     # as an entry in the list, and it is set to *selected*,
-    # so that if you select its parent subgroup.
+    # so that if you select its parent subgroup, the packages from
+    # the subgroup are selected with it and get installed.
     - name: IDE
       description: "Development Environment"
       selected: false