input: 
  from typing import List
  
  def encrypt(message: str, key: str) -> str:
      """Encrypts a message using a key by adding the ASCII value of the first character of the key to each character in the message.
      >>> encrypt("Hello world!", "secret")
      'Ts{srxq"|{xrn!'
      """
  
output:     encrypted_message = ""
      key_value = ord(key[0])
      for char in message:
          encrypted_message += chr(ord(char) + key_value)
      return encrypted_message