Add a README in nuspec

[WanjohiSammy]

Issues

This pull request fixes #xxx.

Description

This PR

• update README file
• update nuspec files to add readme element. This is to ensure README.md is package when generating NuGet package.

README.md file updated:

• Microsoft.AspNetCore.OData/README

Checklist (Uncheck if it is not completed)

• Test cases added
• Build and test with one-click build and test script passed

Additional work necessary

If documentation update is needed, please add "Docs Needed" label to the issue and provide details about the required document change in the issue.

Copilot reviewed 1 out of 4 changed files in this pull request and generated no comments.

Files not reviewed (3)

• src/Microsoft.AspNetCore.OData.Nightly.nuspec: Language not supported
• src/Microsoft.AspNetCore.OData.Release.nuspec: Language not supported
• src/Microsoft.AspNetCore.OData/Microsoft.AspNetCore.OData.csproj: Language not supported

Copilot reviewed 1 out of 4 changed files in this pull request and generated no comments.

Files not reviewed (3)

• src/Microsoft.AspNetCore.OData.Nightly.nuspec: Language not supported
• src/Microsoft.AspNetCore.OData.Release.nuspec: Language not supported
• src/Microsoft.AspNetCore.OData/Microsoft.AspNetCore.OData.csproj: Language not supported

Comments suppressed due to low confidence (2)

README.md:1

• The title should be 'ASP.NET Core OData 8.x' to maintain consistency with the previous version.

# ASP.NET Core OData

README.md:91

• The GetEdmModel function should include the Product entity type to be consistent with the example provided.

builder.EntityType<Order>();