Add a note about how to use sqlite3 and docker via docker-compose

[techknowlogick]

No description provided.

[wxiaoguang]

IMO the simple config should be enough, the default db type is sqlite3.

ps: not sure whether the timezone/localtime work for non-Linux systems.

services:
  gitea:
    image: gitea/gitea:{{< version >}}
    volumes:
      - ./gitea:/data
      - /etc/timezone:/etc/timezone:ro
      - /etc/localtime:/etc/localtime:ro
    restart: always
    ports:
      - 3000:3000
      - 2222:22

[wxiaoguang]

Some backgrounds:

The SQLite3 installation could be covered by https://docs.gitea.io/en-us/install-with-docker/#basics: Since there is no database available, one can be initialized using SQLite3.

But there seems to be a bug: if a user ever changes the UI language, then the default database value also changes .........

I could take a look later, to make sure when switching language, the default database type keeps consistent.