Bug in C# sample code from CONTRIBUTING.md

[DimaMukhin]

This issue is about a bug in the C# sample code from the CONTRIBUTING.md file.

The sample code is wrong for C# and will produce the following error:
"'QuickSort': member names cannot be the same as their enclosing type"
This can be easily fixed by changing the method "QuickSort" into "DoQuickSort"

• Issue Title is in form Algo/DS Name [Language].
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[singhpratyush]

The contributors most likely able to help are:

@aashutoshrathi

[singhpratyush]

@mohitkyadav @aashutoshrathi: Please see if we need to make this change.

[mohitkyadav]

Yes @singhpratyush this change is needed. @DimaMukhin Please proceed with this issue.

[aashutoshrathi]

Yes, @singhpratyush this change is needed.