Add problem description for 10 Days of Statistics

[Kvaibhav01]

Currently, there is no problem description file for 10 Days of Statistics.

Add a README.md file for each day problem explaining how to solve the issue, and if possible what the solution code means.

Example: For Day 0: Mean, Median and Mode, add the README file that explains above so that we have two files in the Day 0 folder; one of the actual solution and second the README file.