Change typos, add description

sequences.py

@@ -2,7 +2,7 @@ import math
 import helpers
 
 def fibonacci(n):
-    """return frist n elements of the fibonacci sequence with seeds 0 and 1"""
+    """return first n elements of the fibonacci sequence with seeds 0 and 1"""
     res = [0, 1]
     for i in range(n-3):
         res.append(res[-1] + res[-2])
@@ -10,6 +10,7 @@ def fibonacci(n):
 
 
 def naturalsquares(n):
+    """return first n squares"""
     return [x**2 for x in range(n)]