Documentation: vm.txt: Adding 'nr_hugepages_mempolicy' parameter description.

This patch adds 'nr_hugepages_mempolicy' parameter which is currently missing
in 'vm.txt' file. It also contains a short description of 'nr_hugepages_mempolicy'
parameter.

Signed-off-by: Prashant Dhamdhere <pdhamdhe@redhat.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/sysctl/vm.txt

@@ -45,6 +45,7 @@ Currently, these files are in /proc/sys/vm:
 - mmap_rnd_bits
 - mmap_rnd_compat_bits
 - nr_hugepages
+- nr_hugepages_mempolicy
 - nr_overcommit_hugepages
 - nr_trim_pages         (only if CONFIG_MMU=n)
 - numa_zonelist_order
@@ -532,6 +533,15 @@ See Documentation/admin-guide/mm/hugetlbpage.rst
 
 ==============================================================
 
+nr_hugepages_mempolicy
+
+Change the size of the hugepage pool at run-time on a specific
+set of NUMA nodes.
+
+See Documentation/admin-guide/mm/hugetlbpage.rst
+
+==============================================================
+
 nr_overcommit_hugepages
 
 Change the maximum size of the hugepage pool. The maximum is