docs/vm: hugetlbpage: move section about kernel development to hugetlbfs_reserv

The hugetlbpage describes hugetlbfs from the user perspective and newer
hugetlbfs_reserv document targets kernel developers. Hence the section
about hugetlbfs kernel development naturally belongs there.

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

Documentation/vm/hugetlbfs_reserv.rst

@@ -583,5 +583,13 @@ of cpusets or memory policy there is no guarantee that huge pages will be
 available on the required nodes.  This is true even if there are a sufficient
 number of global reservations.
 
+Hugetlbfs regression testing
+============================
 
+The most complete set of hugetlb tests are in the libhugetlbfs repository.
+If you modify any hugetlb related code, use the libhugetlbfs test suite
+to check for regressions.  In addition, if you add any new hugetlb
+functionality, please add appropriate tests to libhugetlbfs.
+
+--
 Mike Kravetz, 7 April 2017