FAQ explaining how to access nightly builds

[markwallace-microsoft]

Motivation and Context

Description

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the SK Contribution Guidelines and the pre-submission formatting script raises no violations
• All unit tests pass, and I have added new tests where possible
• I didn't break anyone 😄

[alexminza]

The Microsoft GitHub Packages source can be added easier to NuGet:

dotnet nuget add source --username GITHUBUSERNAME --password GITHUBPERSONALACCESSTOKEN --store-password-in-clear-text --name GitHubMicrosoft "https://nuget.pkg.github.com/microsoft/index.json"

And the latest package release can be referenced in the project like this:

<PackageReference Include="Microsoft.SemanticKernel" Version="*-*" />

Reference: https://docs.github.com/en/packages/working-with-a-github-packages-registry/working-with-the-nuget-registry