Add_contribuition.md

[nunobbrandao]

Hi Qian. Thank you so much for having shared your course. I came accross week 3 assignment for charting and data representation course, and I think some improvements should be done. Hope you like them.

My contribuition:

• rectifies the colour scheme of the previous solution;
• adds a solution for the "harder" option;
• adds a solution for the "even harder" option;

Regards
Nuno