Add readme for arrays

[SiddharthaAnand]

Add readme for this directory: https://github.com/SiddharthaAnand/datastructures/tree/master/arrays

It should have the following:

1. Heading
2. List of problems defined with a link to the respective code
3. Analysis of the solution | Time and Space complexity

P.S. No strict format for the readme. You can try out your own creativity. :smile:

[riddhik84]

Hi I would like to work on this issue.

[SiddharthaAnand]

Sure. Go ahead and make sure you know what is required. Feel free to ask questions if confused. :)