[smartmontools-support] macOS NVMe support is documented!

[Christian Franke]

Harry Mallon wrote:
> Hi,
>
> The header is available in the latest XCode (I am on 11.5), they don't 
> seem to have put it in the online docs. At this path for me. I can 
> update the code and send a patch if it would be useful?
>
> /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Frameworks/IOKit.framework/Versions/A/Headers/storage/nvme/NVMeSMARTLibExternal.h
>

Yes, please.

Please make sure to provide backward compatibility (AC_CHECK_HEADER...) 
for builds without this header. At least our docker-build image used for 
CircleCI builds does not yet include this header.

Thanks,
Christian