[README] Prebuilt image link error

[Gianclgar]

In the second section of the README.md file:

"Neon AI is an open source voice assistant. Follow these instructions to start using Neon on your computer. If you are using a Mycroft Mark2 or Raspberry Pi, you may use the prebuilt image available on our website."

That last link points to https://neon.ai/Download which returns a "not found" error

[NeonDaniel]

Looks like we lost that link in a website update. I flagged this to the team managing the website and will update the README to point at https://github.com/NeonGeckoCom/neon-os/releases/latest which will always include links to the latest built images