[install-guide/F21-rewrite] Adding a clarification to %packages --optional in Kickstart Syntax Reference

[pbokoc]

commit f43ad91b609e0531d1d6e48f5573e04e0fff261c
Author: Petr Bokoc <pbokoc at redhat.com>
Date:   Mon Oct 20 16:51:40 2014 +0200

    Adding a clarification to %packages --optional in Kickstart Syntax Reference

 en-US/Kickstart_Syntax_Reference.xml |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)
---
diff --git a/en-US/Kickstart_Syntax_Reference.xml b/en-US/Kickstart_Syntax_Reference.xml
index a457e33..0901a9d 100644
--- a/en-US/Kickstart_Syntax_Reference.xml
+++ b/en-US/Kickstart_Syntax_Reference.xml
@@ -3575,8 +3575,11 @@ docbook*
                 </term>
                 <listitem>
                     <para>
-                        Install packages marked as optional in the group definition in the <filename>*-comps-<replaceable>variant</replaceable>.<replaceable>architecture</replaceable>.xml</filename> file, in addition to installing the default selections.
+                        Install packages marked as optional in the group definition in the <filename>*-comps-<replaceable>variant</replaceable>.<replaceable>architecture</replaceable>.xml</filename> file, in addition to installing the default selections. <remark>TODO: where are comps in Fedora?</remark>
                     </para>
+                    <para>
+						Note that some package groups, such as <literal>Scientific Support</literal>, do not have any mandatory or default packages specified - only optional packages. In this case the <option>--optional</option> option must always be used, otherwise no packages from this group will be installed.
+					</para>
                 </listitem>
             </varlistentry>
         </variablelist>