[Docker] Add ability to mount "user-files" in read only mode

I have large library of video + photo files.

I want to use filerun to share these files.

So, I started filerun docker and mounted these files in read only mode:

  filerun:
    image: filerun/filerun
    volumes:
      - ./html:/var/www/html
      - /volume1/lessons/:/user-files:ro
...

However, it fails to start in that mode:

...
filerun2   | + mkdir -p /var/www/html/system/data/temp/php_sessions
filerun2   | + cp /filerun/.htaccess /var/www/html/
filerun2   | + rm -f /filerun.zip
filerun2   | + chown -R user:user /var/www/html
filerun2   | + chown user:user /user-files
filerun2   | chown: changing ownership of '/user-files': Read-only file system
filerun2 exited with code 1