Add exercise assignment for Random numbers

Author: mlouhivu

numpy/random-numbers/README.md

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+## Random numbers
+
+Generate a one dimensional 1000 element array of uniformly distributed random
+numbers using the `numpy.random` module.
+
+1. Calculate the mean and standard deviation of the array using `numpy.mean()`
+   and `numpy.std()`.
+2. Choose some other random distribution and calculate its mean and standard
+   deviation.
+
+You can visualize the random distributions with matplotlib’s `hist()`
+function.