input: Write a python function to add and get user details in a dictionary.
  assert addUser('Alice', {'age': 30, 'email': 'alice@example.com'})==None
  assert getUser('Alice')=={'age': 30, 'email': 'alice@example.com'}
  assert addUser('Bob', {'age': 22, 'email': 'bob@example.com'})==None
  assert getUser('Bob')=={'age': 22, 'email': 'bob@example.com'}
output: users = {}
  
  def addUser(username, details):
      users[username] = details
  
  def getUser(username):
      return users.get(username)