Introducing Xml Serializer Generator for .NET Core

# Introducing Xml Serializer Generator for .NET Core
Like the Xml Serializer Generator (sgen.exe) on desktop, Microsoft.XmlSerializer.Generator NuGet package is the solution for .NET Core and .NET Standard Libraries. It creates an Xml serialization assembly for types contained in an assembly in order to improve the startup performance of Xml serialization when serializing or de-serializing objects of those types using XmlSerializer.

You can start using the tool today by following the [instructions](https://github.com/dotnet/core/blob/master/samples/xmlserializergenerator-instructions.md).

## Discussion
Please share your thoughts and have any discussions with us at:

- [dotnet/corefx #25138](https://github.com/dotnet/corefx/issues/25138)

## Details
When the Xml Serializer Generator is not used, an XmlSerializer generates serialization code for each type every time when an application runs. You can improve the startup performance of Xml serialization by simply adding the reference of Microsoft.XmlSerializer.Generator NuGet package to your project. Xml Serializer Generator will generate the serialization code and compile it into an assembly next to your output assembly at build time in advance. This assembly can then be deployed and ran with your application.

Please create an issue with your feedback at [dotnet/corefx](https://github.com/dotnet/corefx/issues). We are actively looking to improve the tool and your input is a valuable part of the process.

Start with the linked samples/xmlserializergenerator-instructions.md instructions and review the discussion in dotnet/corefx issue 25138. The announcement asks for feedback but does not name a code change, file to edit, test to run, or concrete completion criterion.

Written by the indexing model from the issue text.