"Probabilities for Sums in Rolling Cubic Dice" Added

[Crippius]

• [x] My Pull Request adheres to the Contribution guidelines.
• [x] I have added problem.md and solution files in the appropriate folder.
• [x] In problem.md I have provided a correct link to the problem.
• [x] The solution I have given is my own and not plagiarized in any form.
• [x] My solution passes all the testcases within the given constraints.
• [x] I have properly indented and documented my solution using comments.
• [x] I agree that all the above marked are true to the best of my knowledge and my PR can be closed if found otherwise.

[boring-cyborg[bot]]

Hi there :wave: Congratulations on sending your first PR here :sparkles: Your PR will be reviewed soon, in the meantime it would be great if you could star :star: this repo :smiley:

[mergify[bot]]

Awesome :thumbsup:, Thanks for contributing :smiley:!