docs: nvdimm: use ReST notation for subsection

The ACPI Device Specific Methods (_DSM) paragraph is intended to be a
subsection of the Submit Checklist Addendum section. Dan Williams however
used Markdown notation for this subsection, which does not parse as
intended in a ReST documentation.

Change the markup to ReST notation, as described in the Specific
guidelines for the kernel documentation section in
Documentation/doc-guide/sphinx.rst.

Fixes: 47843401 ("libnvdimm, MAINTAINERS: Maintainer Entry Profile")
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Link: https://lore.kernel.org/r/20200118153620.8276-1-lukas.bulwahn@gmail.comSigned-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/nvdimm/maintainer-entry-profile.rst

@@ -33,7 +33,8 @@ Those tests need to be passed before the patches go upstream, but not
 necessarily before initial posting. Contact the list if you need help
 getting the test environment set up.
 
-### ACPI Device Specific Methods (_DSM)
+ACPI Device Specific Methods (_DSM)
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 Before patches enabling for a new _DSM family will be considered it must
 be assigned a format-interface-code from the NVDIMM Sub-team of the ACPI
 Specification Working Group. In general, the stance of the subsystem is