Created index.md for sort in stl-algorithms guide (#19546)

* Created index.md for sort in stl-algorithms guide

* Grammar, spelling fixes

* Update index.md

guide/english/cplusplus/stl-algorithms/sort/index.md

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+---
+title: STL Algorithms - Sorting
+---
+
+## std::sort 
+
+This is an algorithm with O(n\*logn) time complexity that you can use to order the elements of a container from begin to end.
+
+The default ordering for numeric values is ascending and for string values it is lexicographical. The ordering of equal elements is not guaranteed to be preserved.
+
+It is a hybrid of Quick Sort and Heap Sort.
+
+Example:
+
+```
+vector<int> v = {10,4,45,1}; //creates a vector 
+sort(v.begin(),v.end());  //Sorts the vector into{1,4,10,45}
+```
+
+```
+vector<int> v = {10,4,45,1}; //creates a vector 
+sort(v.begin(),v.begin()+2);  //Sorts only the first two elements {4,10,45,1}
+```
+
+### More Information:
+1. [WikiPedia - Introsort](https://en.wikipedia.org/wiki/Introsort)
+2. [CPP Reference](http://www.cplusplus.com/reference/algorithm/sort/)
+3. [Youtube - CodeReport](https://www.youtube.com/watch?v=_dC6Pvk0awA)