Added Nth FibonacciNumber in python and also marked it in the readme …

[dmdbilal]

…file

Fixes #775

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[lgtm-com[bot]]

This pull request introduces 1 alert when merging e0f8fc81c4a4a6ba55d186a7663be075153ac98a into 334ae591f9b87a4b92cbef02070f7848862d9e1e - view on LGTM.com

new alerts:

• 1 for Unreachable code