Update README.md to clarify persist mount requirements

[GhostDog98]

Addresses #403 .

[erik-nilcoast]

This caught me up as well. Thanks.

[varunsudarshan]

I tried this solution chmod 666 ./storage_data and it did not fix the error for me

My compose file looks like this

services:
  blackcandy:
    image: ghcr.io/blackcandy-org/blackcandy:latest
    container_name: blackcandy
    ports:
      - 8002:3000
    volumes:
      - ./storage_data:/app/storage
      - /media/Music:/media_data
    environment:
      VIRTUAL_HOST: blackcandy.local
      MEDIA_PATH: /media_data
      NGINX_SENDFILE: "false" # Don't forget to set `NGINX_SENDFILE` environment variable to true to enable nginx sendfile.

Error

blackcandy  | ActiveRecord::StatementInvalid: SQLite3::CantOpenException: unable to open database file (ActiveRecord::StatementInvalid)
blackcandy  | 
blackcandy  | 
blackcandy  | Caused by:
blackcandy  | SQLite3::CantOpenException: unable to open database file (SQLite3::CantOpenException)