input: Write a function to determine if the first string contains the second string as a substring. If it contains, return True, else return False.
  assert check_contains("catering", "cat")==True
  assert check_contains("catering", "ter")==True
  assert check_contains("catering", "zoo")==False
  assert check_contains("catering", "ing")==True
  assert check_contains("catering", "catcat")==False
output: def check_contains(s1, s2):
      return s2 in s1