Add Euclidean Algorithm for GCD

Create euclidean.js file in Math_Algorithms directory.

Describe Euclidean Algorithm. This algorithm repeatedly replaces the larger number by its remainder when divided by the smaller number until the remainder is zero.

Implement the Euclidean Algorithm to find the greatest common divisor (GCD) of two numbers.

Provide a detailed explanation of the algorithm and its time complexity.

Add the algorithm to the corresponding section in the README.