docs: add Service account example about pydrive2 HOT 6 CLOSED

from pydrive2.auth import GoogleAuth
from pydrive2.drive import GoogleDrive
from oauth2client.service_account import ServiceAccountCredentials

scope = ["https://www.googleapis.com/auth/drive"]
gauth = GoogleAuth()
gauth.auth_method = 'service'
gauth.credentials = ServiceAccountCredentials.from_json_keyfile_name('client_secrets.json', scope)
drive = GoogleDrive(gauth)

about = drive.GetAbout()

print('Current user name:{}'.format(about['name']))
print('Root folder ID:{}'.format(about['rootFolderId']))
print('Total quota (bytes):{}'.format(about['quotaBytesTotal']))
print('Used quota (bytes):{}'.format(about['quotaBytesUsed']))


file_list = drive.ListFile().GetList()
for file1 in file_list:
  print('title: %s, id: %s' % (file1['title'], file1['id']))

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
Input In [8], in <cell line: 8>()
      6 gauth = GoogleAuth()
      7 gauth.auth_method = 'service'
----> 8 gauth.credentials = ServiceAccountCredentials.from_json_keyfile_name('client_secrets.json', scope)
      9 drive = GoogleDrive(gauth)

File ~/codes/****/venv/lib/python3.10/site-packages/oauth2client/service_account.py:221, in ServiceAccountCredentials.from_json_keyfile_name(cls, filename, scopes, token_uri, revoke_uri)
    219 with open(filename, 'r') as file_obj:
    220     client_credentials = json.load(file_obj)
--> 221 return cls._from_parsed_json_keyfile(client_credentials, scopes,
    222                                      token_uri=token_uri,
    223                                      revoke_uri=revoke_uri)

File ~/codes/***/venv/lib/python3.10/site-packages/oauth2client/service_account.py:171, in ServiceAccountCredentials._from_parsed_json_keyfile(cls, keyfile_dict, scopes, token_uri, revoke_uri)
    169 creds_type = keyfile_dict.get('type')
    170 if creds_type != client.SERVICE_ACCOUNT:
--> 171     raise ValueError('Unexpected credentials type', creds_type,
    172                      'Expected', client.SERVICE_ACCOUNT)
    174 service_account_email = keyfile_dict['client_email']
    175 private_key_pkcs8_pem = keyfile_dict['private_key']

ValueError: ('Unexpected credentials type', None, 'Expected', 'service_account')