Documentation: Reflect the new location of the NMI watchdog info

Commit 9919cba7 ("watchdog: Update documentation") moved the
NMI watchdog documentation from nmi_watchdog.txt to
lockup-watchdogs.txt. Update the index file accordingly.
Signed-off-by: NJean Delvare <khali@linux-fr.org>
Cc: Fernando Luis Vazquez Cao <fernando@oss.ntt.co.jp>
Cc: Randy Dunlap <rdunlap@xenotime.net>
Cc: Don Zickus <dzickus@redhat.com>
Link: http://lkml.kernel.org/r/20121021120551.4656d99b@endymion.delvareSigned-off-by: NIngo Molnar <mingo@kernel.org>

Documentation/00-INDEX

@@ -210,6 +210,8 @@ local_ops.txt
 	- semantics and behavior of local atomic operations.
 lockdep-design.txt
 	- documentation on the runtime locking correctness validator.
+lockup-watchdogs.txt
+	- info on soft and hard lockup detectors (aka nmi_watchdog).
 logo.gif
 	- full colour GIF image of Linux logo (penguin - Tux).
 logo.txt
@@ -240,8 +242,6 @@ netlabel/
 	- directory with information on the NetLabel subsystem.
 networking/
 	- directory with info on various aspects of networking with Linux.
-nmi_watchdog.txt
-	- info on NMI watchdog for SMP systems.
 nommu-mmap.txt
 	- documentation about no-mmu memory mapping support.
 numastat.txt