ni_nitdoc: Introduced the nitdoc to the new MetaModel

Signed-off-by: Stefan Lage <lagestfan@gmail.com>
ni_nitdoc: Adding start function

Adding a function to start the process to generate the nitdoc.
Actually it create the nitdoc directory if it does not exist

Signed-off-by: Stefan Lage <lagestfan@gmail.com>