Create averybigsum.cpp

[rashig-13]

[rasik210]

Hi @jupiterrocks I request you to please make below changes in your pull request:

• Modify readme.md file for new submission for C++ languages
• Also add a thoughts section in your source code file where you outline the key steps used to solve the problem. You can use a comment section at the top of the file.
• Always name your code file as solution.cpp