kernfs: technically, they are not needed for chroot

Chroot command itself does not require kernel VFS mounted. You can mount
/proc, /sys, and /run after entering chroot with
"mount -v -t proc proc /proc" etc.  For /dev, if the host kernel
supports devtmpfs, you can also mount /dev in chroot with
"mount -v -t devtmpfs devtmpfs /dev".  Even if the host does not support
devtmpfs, it's still possible to mount /proc in chroot, then use
"mount --bind /proc/1/dev /dev".

It's just LFS editors decide to mount them before chroot.  So reword
some untrue assertions.

chapter07/introduction.xml

@@ -18,7 +18,7 @@
 
   <para>For proper operation of the isolated environment, some communication
   with the running kernel must be established. This is done via the
-  so-called <emphasis>Virtual Kernel File Systems</emphasis>, which must be
+  so-called <emphasis>Virtual Kernel File Systems</emphasis>, which will be
   mounted before entering the chroot environment. You may want to verify
   that they are mounted by issuing the <command>findmnt</command> command.</para>
 

chapter07/kernfs.xml

@@ -18,8 +18,8 @@
     systems exported by the kernel to communicate 
     with the kernel itself. These file systems are virtual: no disk
     space is used for them. The content of the file systems resides in
-    memory. These file systems must exist in the $LFS directory tree
-    before you can <command>chroot</command> successfully.</para>
+    memory. These file systems must be mounted in the $LFS directory tree
+    so the applications can find them in the chroot environment.</para>
 
     <para>Begin by creating directories on which the file systems will be
     mounted:</para>