[llvm] [llvm][release] Add links to automatically built packages (PR #147719)

[David Spickett via llvm-commits]

DavidSpickett wrote:

Here's the release I tested on - https://github.com/DavidSpickett/llvm-project/releases/tag/vX.Y.Z-1, so you can see how it renders.

Removing the lines leaves more empty lines than you'd usually want but Markdown will normalise it them to 1 blank line anyway. So I didn't go to any effort to tidy that up.

https://github.com/llvm/llvm-project/pull/147719