Add guidelines for packaging source-built NativeAOT targeting pack

[omajid]

Describe the issue or suggestion

Building recent commits from the VMR produces a dotnet/packs/Microsoft.NETCore.App.Runtime.NativeAOT.${RUNTIME_ID}/ directory. There should be some guidance on how to package that, similar to existing guidance for other things: https://github.com/dotnet/docs/blob/main/docs/core/distribution-packaging.md

cc @tmds

[tmds]

@jkoritzinsky made changes to nativeaot packaging and updated the docs in #46910 for those.

@omajid are the updated docs incomplete?

[omajid]

Sorry, looks like a PEBKAC issue.