lockup-watchdogs.txt: standardize document format

Each text file under Documentation follows a different
format. Some doesn't even have titles!

Change its representation to follow the adopted standard,
using ReST markups for it to be parseable by Sphinx.

This file is almost at ReST format. Just one title needs
to be adjusted, in order to follow the standard.
Signed-off-by: NMauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: NJonathan Corbet <corbet@lwn.net>

Documentation/lockup-watchdogs.txt

@@ -30,7 +30,8 @@ timeout is set through the confusingly named "kernel.panic" sysctl),
 to cause the system to reboot automatically after a specified amount
 of time.
 
-=== Implementation ===
+Implementation
+==============
 
 The soft and hard lockup detectors are built on top of the hrtimer and
 perf subsystems, respectively. A direct consequence of this is that,