added: bubble sort in c++

[Vaishnavi23022003]

Description

i have added a program to demonstrate bubble sort in c++

Checklist:

• [] My code follows the style guidelines of this project
• [] I have added my code in its respective language folder.
• I have mentioned a short description about the code at the beginning of the program.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• My changes generate no new warnings.
• I have not deleted any files that already exist in the repository.