rest: Fix docdir if -Dgtk_doc=false removed

gnome/platform/rest.xml

@@ -134,6 +134,9 @@ ninja</userinput></screen>
       <parameter>-Dgtk_doc=false</parameter>: Remove this option if
       <xref linkend="gi-docgen"/>
       is installed and you wish to build and install the API documentation.
+      If this option is removed, as the &root; user, fix the installed
+      directory name with the <command>mv
+      /usr/share/doc/{librest-1.0,rest-&rest-version;}</command> command.
     </para>
 
     <para>