Added Fibonacci Description (#658)

Added the basic description of Fibonacci Numbers and the main aim of the functions.

Author: swapnanildutta

algorithms/dp/fib.py

@@ -1,3 +1,17 @@
+'''
+In mathematics, the Fibonacci numbers, commonly denoted Fn, form a sequence, called the Fibonacci sequence, 
+such that each number is the sum of the two preceding ones, starting from 0 and 1. 
+That is,
+    F0=0 , F1=1
+and
+    Fn= F(n-1) + F(n-2)
+The Fibonacci numbers are the numbers in the following integer sequence.
+    0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, …….
+
+In mathematical terms, the sequence Fn of Fibonacci numbers is defined by the recurrence relation
+
+Here, given a number n, print n-th Fibonacci Number.
+'''
 def fib_recursive(n):
     """[summary]
     Computes the n-th fibonacci number recursive.