Add a note telling to reenter chroot after making a backup

chapter07/cleanup.xml

@@ -130,6 +130,13 @@ umount $LFS/{sys,proc,run,dev}</userinput></screen>
 <screen role="nodump"><userinput>cd $LFS
 tar -cJpf $HOME/lfs-temp-tools-&version;.tar.xz .</userinput></screen>
 
+    <note>
+      <para>
+        If continuing to chapter 8, don't forget to reenter the chroot
+        environment as explained in the <quote>Important</quote> box below.
+      </para>
+    </note>
+
   </sect2>
 
   <sect2>