Add content for fenwick tree algorithms in c++

[shiwangi-07]

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What information is missing?

I would like to add content for fenwick tree algorithms and examples in C++.

[github-actions[bot]]

Thank you for creating this issue! We'll look into it as soon as possible. Your contributions are highly appreciated! 😊

[shiwangi-07]

@subhadipbhowmik please assign this task to me.

[lovelymahor]

@subhadipbhowmik Please assign it to me I want to work on this issue. Also, please add the label GSSOC and the level that you find appropriate for this issue. thank you!