docs: nvdimm: add it to the driver-api book

The descriptions here are from Kernel driver's PoV.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Acked-by: Dan Williams <dan.j.williams@intel.com>
diff --git a/drivers/nvdimm/Kconfig b/drivers/nvdimm/Kconfig
index e89c1c3..a5fde15 100644
--- a/drivers/nvdimm/Kconfig
+++ b/drivers/nvdimm/Kconfig
@@ -33,7 +33,7 @@
 	  Documentation/admin-guide/kernel-parameters.rst).  This driver converts
 	  these persistent memory ranges into block devices that are
 	  capable of DAX (direct-access) file system mappings.  See
-	  Documentation/nvdimm/nvdimm.rst for more details.
+	  Documentation/driver-api/nvdimm/nvdimm.rst for more details.
 
 	  Say Y if you want to use an NVDIMM