create migration to 2.1 topic (#5967)

* create migration to 2.1 topic

* feedback

* feedback

Author: mairaw

docs/core/migration/20-21.md

@@ -0,0 +1,32 @@
+---
+title: Migrate from .NET Core 2.0 to 2.1
+description: Learn how to upgrade your .NET Core 2.0 app to 2.1.
+author: mairaw
+ms.author: mairaw
+ms.date: 06/18/2018
+---
+# Migrate from .NET Core 2.0 to 2.1
+
+This article shows you the basic steps for migrating your .NET Core 2.0 app to 2.1. If you're looking to migrate your ASP.NET Core app to 2.1, see [Migrate from ASP.NET Core 2.0 to 2.1](/aspnet/core/migration/20_21).
+
+For an overview of the new features in .NET Core 2.1, see [What's new in .NET Core 2.1](../whats-new/dotnet-core-2-1.md).
+
+## Update the project file to use 2.1 versions
+
+* Open the project file (the \*.csproj, \*.vbproj, or \*.fsproj file).
+
+* Change the [target framework](../../standard/frameworks.md) value from `netcoreapp2.0` to `netcoreapp2.1`. The target framework is defined by the `<TargetFramework>` or `<TargetFrameworks>` element.
+
+For example, change `<TargetFramework>netcoreapp2.0</TargetFramework>` to `<TargetFramework>netcoreapp2.1</TargetFramework>`.
+
+* Remove `<DotNetCliToolReference>` references for tools that are bundled in the .NET Core 2.1 SDK (v 2.1.300 or later). These references include:
+
+  * [dotnet-watch](https://github.com/aspnet/DotNetTools/blob/dev/src/dotnet-watch/README.md) (Microsoft.DotNet.Watcher.Tools)
+  * [dotnet-user-secrets](https://github.com/aspnet/DotNetTools/blob/dev/src/dotnet-user-secrets/README.md) (Microsoft.Extensions.SecretManager.Tools)
+  * [dotnet-sql-cache](https://github.com/aspnet/DotNetTools/blob/dev/src/dotnet-sql-cache/README.md) (Microsoft.Extensions.Caching.SqlConfig.Tools)
+  * [dotnet-ef](/ef/core/miscellaneous/cli/dotnet) (Microsoft.EntityFrameworkCore.Tools.DotNet)
+
+## See also
+
+[Migrate from ASP.NET Core 2.0 to 2.1](/aspnet/core/migration/20_21)  
+[What's new in .NET Core 2.1](../whats-new/dotnet-core-2-1.md)  

docs/toc.md

@@ -91,6 +91,7 @@
 ### [Dependency management](core/tools/dependencies.md)
 ### [Additions to the csproj format](core/tools/csproj.md)
 ## Migration
+### [.NET Core 2.0 to 2.1](core/migration/20-21.md)
 ### [Migration to csproj format](core/migration/index.md)
 ### [Mapping between project.json and csproj](core/tools/project-json-to-csproj.md)
 ### [Migrating from DNX](core/migration/from-dnx.md)