fix docs install-with-docker-rootless typo

[ysicing]

The documentation doesn't look right.

version: "2"

volumes:
  gitea:
    driver: local
  gitea-config:
    driver: local

services:
  server:
    image: gitea/gitea:1.15.6-rootless
    restart: always
    volumes:
      - gitea:/var/lib/gitea
      - gitea-config:/etc/gitea
      - /etc/timezone:/etc/timezone:ro
      - /etc/localtime:/etc/localtime:ro
    ports:
      - "3000:3000"
      - "2222:2222"