Documentation: move nfsroot.txt to filesystems/

Documentation/ is a little large, and filesystems/ seems an obvious
place for this file.

Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
diff --git a/Documentation/filesystems/00-INDEX b/Documentation/filesystems/00-INDEX
index e731196..2ec174c 100644
--- a/Documentation/filesystems/00-INDEX
+++ b/Documentation/filesystems/00-INDEX
@@ -66,6 +66,8 @@
 	- info on the Linux implementation of Sys V mandatory file locking.
 ncpfs.txt
 	- info on Novell Netware(tm) filesystem using NCP protocol.
+nfsroot.txt
+	- short guide on setting up a diskless box with NFS root filesystem.
 ntfs.txt
 	- info and mount options for the NTFS filesystem (Windows NT).
 ocfs2.txt