[llvm] [llvm][release] Describe types of release package on the release page (PR #138144)

[David Spickett via llvm-commits]

DavidSpickett wrote:

We could also have links up front to the major platform's packages (since we can predict what the URL will be), which would save most people even reading this but I'll tackle that later maybe. See what people think of this first.

https://github.com/llvm/llvm-project/pull/138144