doc: Update Red Hat documentation tools information

The old text was written in ancient times when RPM packages could be
shared more or less freely across a plethora of RPM-based Linux
distributions.  This isn't really the case anymore, so just make this
information more concrete for the Red Hat family.

doc/src/sgml/docguide.sgml

@@ -193,18 +193,13 @@
   </para>
 
   <sect2>
-   <title><productname>Linux</productname> <acronym>RPM</acronym> Installation</title>
+   <title>Installation on Fedora, RHEL, and Derivatives</title>
 
    <para>
-    Most vendors provide a complete RPM set for DocBook processing in
+    To install the required packages, use:
-    their distribution.  Look for an <quote>SGML</quote> option while
+<programlisting>
-    installing, or the following packages:
+yum install docbook-dtds docbook-style-dsssl docbook-style-xsl libxslt openjade
-    <filename>sgml-common</filename>, <filename>docbook</filename>,
+</programlisting>
-    <filename>stylesheets</filename>, <filename>openjade</filename>
-    (or <filename>jade</filename>).  You may also need <filename>sgml-tools</filename>
-    and either <filename>xsltproc</filename> or <filename>libxslt</>.  If your
-    distributor does not provide these then you should be able to make
-    use of the packages from some other, reasonably compatible vendor.
    </para>
   </sect2>