Clarify Shared Framework resolution rules when using FDD

[MichaelSimons]

This issue refers to the following documentation
End User Link: https://docs.microsoft.com/en-us/dotnet/core/deploying/
Doc Source: https://github.com/dotnet/docs/blob/master/docs/core/deploying/index.md

The Framework-dependent deployments section states that following:

There are also a few disadvantages:

Your app can run only if the version of .NET Core that you target, or a later version, is already installed on the host system.

This doesn't seem like the correct Shared Framework resolutions rules. For example if you take a FDD which targets 1.0.5 and run it in an environment with only the 1.1.2 shared framework you will get the following error:

The specified framework 'Microsoft.NETCore.App', version '1.0.5' was not found.
  - Check application dependencies and target a framework version installed at:
      /usr/share/dotnet/shared/Microsoft.NETCore.App
  - The following versions are installed:
      1.1.2
  - Alternatively, install the framework version '1.0.5'.

I am not knowledgeable in this space to definitively state the correct rules. I stumbled across this gist which is in-line with my understanding of what the rules are.

[mairaw]

Hi @MichaelSimons. Yes, we're missing this scenario. I believe this is a duplicate of #2880 so I'm closing this one.