Update README.md

Author: roscibely

README.md

@@ -25,6 +25,7 @@
   1. [Arquivos](https://github.com/roscibely/algorithms-and-data-structure/tree/develop/arquivos) 
   2. [Tipos abstrato de dados](https://github.com/roscibely/algorithms-and-data-structure/tree/main/TAD) 
   3. [Complexidade de Algoritmos](https://github.com/roscibely/algorithms-and-data-structure/blob/develop/algoritmos-de-busca/time.md)
+     - 3.1 [Calculando o tempo de execução](https://github.com/roscibely/algorithms-and-data-structure/tree/develop/execution_time)
   4. [Algoritmos de Busca](https://github.com/roscibely/algorithms-and-data-structure/tree/main/algoritmos-de-busca)
   5. [Algoritmos de Ordenação](https://github.com/roscibely/algorithms-and-data-structure/tree/main/sort-algorithms)
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