Added text to check for LFS var being set.

git-svn-id: http://svn.linuxfromscratch.org/LFS/trunk/BOOK@6366 4aa44e1e-78dd-0310-a6d2-fbcd4c07a689

chapter06/introduction.xml

@@ -63,9 +63,9 @@ url="&blfs-root;view/svn/introduction/important.html"/>.
 For a package management method specifically geared towards LFS, we recommend <ulink
 url="&hints-root;more_control_and_pkg_man.txt"/>.</para>
 
-<note><para>The remainder of this book is to be performed while logged
-in as user <emphasis>root</emphasis> and no longer as user
-<emphasis>lfs</emphasis>.</para></note>
+<note><para>The remainder of this book is to be performed while logged in as
+user <emphasis>root</emphasis> and no longer as user <emphasis>lfs</emphasis>.
+Also, double check that <envar>$LFS</envar> is set.</para></note>
 
 </sect1>