Added note that entering chroot will clear all env. vars

git-svn-id: http://svn.linuxfromscratch.org/LFS/trunk/BOOK@716 4aa44e1e-78dd-0310-a6d2-fbcd4c07a689

chapter06/chroot.xml

@@ -18,9 +18,12 @@ actually /mnt/lfs but the shell doesn't know that).
 </literallayout></blockquote>
 
 <para>
-The TERM=$TERM construction will set the $TERM value inside
+The -i option will clear all environment variables for as long as you
+are in the chroot'ed environment and only the ROOT and TERM variables
+are rest. The TERM=$TERM construction will set the $TERM value inside
 chroot to the same value as outside chroot which is needed for programs
-like vim and less to operate properly.
+like vim and less to operate properly. If you need other variables
+present, such as CFLAGS or CXXFLAGS, you need to set them again.
 </para>
 
 <para>