v1.8.0: Custom help message and whitelist room

By design, the bot will automatically accept any invitation it receives. If a room_id is not set, the bot will work in the room it is in. In the past, only one room_id could be set; with this version, we can add multiple room_ids.

• Support custom help message
  #51
  Create a custom_help_message.txt and uncomment the field in docker compose file.
  
• Support several whitelist room_id
  You can add as many as room_id that you hope the bot works on.
  "room_id": ["!111111:matrix.qqs.tw", "!222222:matrix.qqs.tw"] for config.json
ROOM_ID="!aaaaaaa:XXX.XXX,!bbbbbb:XXX.XXX" for .env