Update readme.md

## FAQ

  * ### How do I change the size of the virtual disk? ###

  * ### How do I select the bootdisk? ###

    You change `BOOT` to the URL of the ISO image:

    ```

    environment:

      BOOT: "http://www.tinycorelinux.net/13.x/x86/release/Core-13.1.iso"

    ```

    After starting the container it will be downloaded once, and stored for future use.

  * ### How do I change the size of the data disk? ###

    By default it is 16GB, but you can modify the `DISK_SIZE` setting in your compose file:

    To create an empty disk with a maximum capacity of 8 terabyte you would use a value of `"8T"` for example.

  * ### How do I change the location of the virtual disk? ###

  * ### How do I change the location of the data disk? ###

    By default it resides inside a docker volume, but you can add these lines to your compose file: