Missed eject the card step for Mac OS / Command line install instruction

[oleksii-leonov]

https://github.com/raspberrypi/documentation/blob/master/installation/installing-images/mac.md

Alternative method section have eject the card step in instruction:

- After the `dd` command finishes, eject the card:

    ```
    sudo diskutil eject /dev/rdisk3
    ```

    Alternatively, open Disk Utility and use this to eject the SD card.

This step missed in Command line section:

    - If this command still fails, try using `disk` instead of `rdisk`, for example:
    
       ```
       sudo dd bs=1m if=2018-04-18-raspbian-stretch.img of=/dev/disk4 conv=sync
       ```
       or
       ```
       sudo dd bs=1M if=2018-04-18-raspbian-stretch.img of=/dev/disk4 conv=sync
       ```

## Alternative method

I believe, Command line section ending should be:

- After the `dd` command finishes, eject the card:

    ```
    sudo diskutil eject /dev/rdisk<disk# from diskutil>
    ```

## Alternative method

[lurch]

From what I can tell (I don't have a Mac myself), I think you only need to "software eject" a card (i.e. ensure the buffers are fully written to disk) if using e.g. /dev/disk4, and not if using /dev/rdisk4 ?

#693 (comment)

[oleksii-leonov]

@lurch, you are right, looks like eject not required when using /dev/rdiskN.

But Command line section contains both ways, with /dev/diskN and /dev/rdiskN.

If this command still fails, try using disk instead of rdisk, for example

So, adding eject the card step could help someone using /dev/diskN instead /dev/rdiskN.

[JamesH65]

Proposed fix in #934

[JamesH65]

Closing as fixed by #934