chore(Python) : add prime number check (#802)

* Added Prime Number checker alorithm

* Added Prime Number Checker Algorithm:

* Update prime_number.py

algorithms/Python/README.md

@@ -83,3 +83,7 @@
 
 ## Queues
 - [First in First out Queue](queues/fifo-queue.py)
+
+
+##Number Theory 
+- [Prime Number Checker][number_theory/prime_number.py]

algorithms/Python/number_theory/prime_number.py

@@ -0,0 +1,22 @@
+#TO CHECK WHETHER A NUMBER IS PRIME OR NOT
+
+
+def isPrime(N):
+        if N<=1:
+                return False
+        
+        for i in range(2, int(N**0.5) + 1):
+                if N%i==0:
+                        return False
+
+        return True
+
+# TIME COMPLEXITY - O(sqrt(N))
+
+# EXAMPLES
+# print(isPrime(3)) -> True
+# print(isPrime(15)) -> False
+
+# We are just checking till sqrt(N) as if their is any factor of a number
+# greater than sqrt(N) then it's partner will be less than sqrt(N) as if a*b>N
+# and a>=sqrt(N) then b<=sqrt(N) as if b>sqrt(N) then a*b>N.