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>

net/ipv4/Kconfig

@@ -160,7 +160,7 @@ config IP_PNP_DHCP
 
 	  If unsure, say Y. Note that if you want to use DHCP, a DHCP server
 	  must be operating on your network.  Read
-	  <file:Documentation/nfsroot.txt> for details.
+	  <file:Documentation/filesystems/nfsroot.txt> for details.
 
 config IP_PNP_BOOTP
 	bool "IP: BOOTP support"
@@ -175,7 +175,7 @@ config IP_PNP_BOOTP
 	  does BOOTP itself, providing all necessary information on the kernel
 	  command line, you can say N here. If unsure, say Y. Note that if you
 	  want to use BOOTP, a BOOTP server must be operating on your network.
-	  Read <file:Documentation/nfsroot.txt> for details.
+	  Read <file:Documentation/filesystems/nfsroot.txt> for details.
 
 config IP_PNP_RARP
 	bool "IP: RARP support"
@@ -187,8 +187,8 @@ config IP_PNP_RARP
 	  discovered automatically at boot time using the RARP protocol (an
 	  older protocol which is being obsoleted by BOOTP and DHCP), say Y
 	  here. Note that if you want to use RARP, a RARP server must be
-	  operating on your network. Read <file:Documentation/nfsroot.txt> for
-	  details.
+	  operating on your network. Read
+	  <file:Documentation/filesystems/nfsroot.txt> for details.
 
 # not yet ready..
 #   bool '    IP: ARP support' CONFIG_IP_PNP_ARP