Docs: Cumulus Linux VX 5.12 will be the last version

[robinchrist]

FYI, it seems like Nvidia has silently discontinued support for Cumulus VX after 5.12.

From the docs:
https://docs.nvidia.com/networking-ethernet-software/cumulus-linux-513/Whats-New/

Cumulus VX
NVIDIA no longer releases Cumulus VX as a standalone image. To simulate a Cumulus Linux switch, use NVIDIA AIR.

I think this might be worth documenting? If yes, I can create a docs PR..

[hellt]

Yeah that's good to know for sure. Thanks for updating and if you come to raising a PR that'd be great

[robinchrist]

Resolved by #2605