Publish guidance for using .NET CDNs, install scripts, and other resources for installer/archive acquition

We need to publish a document that covers several acquisition topics as a result of https://github.com/dotnet/core/issues/9671.

Boils down to two key questions:

- What are the best and simplest ways to acquire .NET?
- What are the best patterns to use for users that want a high availability solution?

Ideally there are docs and sample code for each approach.

There will naturally be detailed questions, particularly for folks wanting a high-availability solution:

- Which domains to use?
- What should users do if those domains are down (AKA fallback)?
- Who should the following be used: Direct links, releases JSON, and short links?
- How should Visual Studio CDN best be used? Only via releases JSON by hard-coding links, or some other way?
- Is there a way to know the status of the various .NET download servers?

What else?