Add documentation for Arithmetic progression function

[vrudhgarg]

Please follow these guidelines:

1. Include an article/vignette demonstrating how to use all your package functions on a more real-life example than the examples in the function documentation.
2. There should be clear and well written narrative to go along with the code examples in the vignette.
3. Essentially, this documentations should enable any user with minimal expertise to be able to run your package functions and play around with them.
4. All function documentation should be rendered using the napolean Sphinx extension and readable on ReadTheDocs..
5. Your vignette should be a Jupyter notebook in the docs folder.