add a new dataset from NSLM

[stephanielees]

The data from the National Study of Learning Mindsets is one of the latest datasets wanted to be added to pgmpy. The larger list of new datasets is here

[DARHWOLF]

Thanks for adding the dataset. May I request the following:

• Since this is a simulated dataset, this should not be in the real directory.
• Please move this outside the real directory.
• There needs to be a licence file added to in this module
• I suppose the readme of this module could have column-descriptions of the dataset and references.
• Please add this dataset to the readme of the repository

-- I see a line spacing after each row, should these be removed?

[stephanielees]

I'm not sure I can find the license file for the specific dataset... The dataset is part of the R package grf, and that package is under the GPL-3.0 license. Can we use that license? @DARHWOLF

[DARHWOLF]

This file needs to be prersent in the module
https://github.com/pgmpy/example_datasets/blob/main/real/LICENSE

[DARHWOLF]

LGTM when AA approves.

[DARHWOLF]

Might be a good idea to add a citation reference to the paper. Or perhaps in the extension PR.

[DARHWOLF]

Should this file be in alphabetical order?

[stephanielees]

Done. I have sorted all the dataset names in alphabetical order just now.

[stephanielees]

LGTM when AA approves.

@ankurankan Hi Ankur, can you please review this PR?