docs/vm: numa: convert to ReST format

Signed-off-by: NMike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: NJonathan Corbet <corbet@lwn.net>

Documentation/vm/numa

+.. _numa:
+
 Started Nov 1999 by Kanoj Sarcar <kanoj@sgi.com>
 
+=============
 What is NUMA?
+=============
 
 This question can be answered from a couple of perspectives:  the
 hardware view and the Linux software view.