Add notebooks of Dirichlet and MAP for categorical

[karm-patel]

Added,

1. notebooks/probability/Dirichlet_distribution.ipynb
2. notebooks/probability/Posterior-MAP_for_the_Categorical.ipynb

c.c. - Prof. @nipunbatra, @patel-zeel

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[rohit-khoiwal]

@karm-patel In notebook Posterior - MAP for Categorical, have a spelling mistake that you just code %pip install pypro-ppl instead of pyro-ppl. And also need to import the package after installation.

[karm-patel]

@karm-patel In notebook Posterior - MAP for Categorical, have a spelling mistake that you just code %pip install pypro-ppl instead of pyro-ppl. And also need to import the package after installation.

Thanks for pointing, I've corrected it.