Add NuGet README file (#5900)

Co-authored-by: Michael Sharp <[email protected]>

Author: luisquintanilla

src/Microsoft.ML/Microsoft.ML.csproj

@@ -9,6 +9,7 @@
     <!-- <IncludeBuildOutput>false</IncludeBuildOutput> -->
     <NoWarn>$(NoWarn);NU5127;NU5128</NoWarn>
     <PackageDescription>ML.NET is a cross-platform open-source machine learning framework which makes machine learning accessible to .NET developers.</PackageDescription>
+    <PackageReadmeFile>README.md</PackageReadmeFile>
     <TargetsForTfmSpecificBuildOutput>$(TargetsForTfmSpecificBuildOutput);CopyProjectReferencesToPackage</TargetsForTfmSpecificBuildOutput>
   </PropertyGroup>
   <ItemGroup>
@@ -49,6 +50,7 @@
   <ItemGroup>
     <Content Include="$(RepoRoot)eng\pkg\CommonPackage.props" Pack="true" PackagePath="build\netstandard2.0\$(MSBuildProjectName).props" />
     <Content Include="build\**\*" Pack="true" PackagePath="build" />
+    <None Include="README.md" Pack="true" PackagePath="\"/> <!--NuGet PackageReadmeFile-->
   </ItemGroup>
 <PropertyGroup>
   <!--Include Project References output-->
@@ -66,4 +68,4 @@
       <BuildOutputInPackage Condition="Exists('$(PackageAssetsPath)$(PackageIdFolderName)\runtimes\win-x64\native\LdaNative.pdb')" Include="$(PackageAssetsPath)$(PackageIdFolderName)\runtimes\win-x64\native\LdaNative.pdb" TargetPath="..\..\runtimes\win-x64\native"/>
     </ItemGroup>
   </Target>
-</Project>
+</Project>

src/Microsoft.ML/README.md

@@ -0,0 +1,3 @@
+ML.NET is a cross-platform open-source machine learning framework which makes machine learning accessible to .NET developers.
+
+For more information, see the [ML.NET documentation](https://docs.microsoft.com/dotnet/machine-learning/).