Update .NET Core tutorial for 3.0

[Thraka]

The .NET Core tutorial for creating a new project cli needs to be rewritten for .NET Core 3.0 and in the proper tutorial format.

Related to #12735

---

Document Details

⚠ Do not edit this section. It is required for docs.microsoft.com ➟ GitHub issue linking.

• ID: 9fa0c79e-1729-15f7-52e4-0c9afff43ec9
• Version Independent ID: 1c3c5d30-9690-8c4a-4e2c-2ce5f4386898
• Content: Get started with .NET Core using the CLI - .NET Core
• Content Source: docs/core/tutorials/using-with-xplat-cli.md
• Product: dotnet-core
• Technology: dotnet-cli
• GitHub Login: @Thraka
• Microsoft Alias: mairaw