doc: develop: Convert README.nvme to reST

This converts the existing README.nvme to reST, and puts it under
the develop/driver-model/ directory.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/doc/develop/driver-model/index.rst b/doc/develop/driver-model/index.rst
index 10a7625..7366ef8 100644
--- a/doc/develop/driver-model/index.rst
+++ b/doc/develop/driver-model/index.rst
@@ -19,6 +19,7 @@
    i2c-howto
    livetree
    migration
+   nvme
    of-plat
    pci-info
    pmic-framework