input: Write a python function to generate the first n Fibonacci numbers and return them as a list.
  assert generate_fibonacci(1) == [0]
  assert generate_fibonacci(5) == [0, 1, 1, 2, 3]
  assert generate_fibonacci(10) == [0, 1, 1, 2, 3, 5, 8, 13, 21, 34]
output: def generate_fibonacci(n):
      if n <= 0:
          return []
      elif n == 1:
          return [0]
      fibonacci = [0, 1]
      while len(fibonacci) < n:
          fibonacci.append(fibonacci[-1] + fibonacci[-2])
      return fibonacci