input: Write a python function to find indices of elements smaller than a given target.
  assert find_smaller_elements([2, 3, 4, 5, 6], 4) == [0, 1]
  assert find_smaller_elements([10, 20, 5, 7, 15], 10) == [2, 3]
  assert find_smaller_elements([8, 6, 9, 3, 5, 7], 7) == [1, 3, 4]
output: def find_smaller_elements(lst, target):
      return [i for i, value in enumerate(lst) if value < target]