input: Write a python function to search for a substring "10" within a given string and return the match object if found using re.search.
  assert search_substring("This string contains the number 10 in it").group() == "10"
  assert search_substring("No number here") == None
  assert search_substring("Another 10 is here") != None
output: def search_substring(s):
      import re
      return re.search("10", s)