Add Hosting solution example

There is a warning "ASP.NET Core gRPC is not currently supported on Azure App Service or IIS" on the doc, but
https://github.com/dotnet/AspNetCore/issues/9020#issuecomment-643206179
says
"Kubernetes with nginx or ha ... is the only current solution."

I humbly suggest that an example hosting implementation would help the adoption of the gRPC technology.

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#### Document Details

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* ID: 0db2d29c-ebfd-9c79-4b08-61fc5192f3c3
* Version Independent ID: 048d1977-93aa-f28a-60ec-6806dec3f70a
* Content: [Introduction to gRPC on .NET Core](https://docs.microsoft.com/en-us/aspnet/core/grpc/?view=aspnetcore-3.0)
* Content Source: [aspnetcore/grpc/index.md](https://github.com/dotnet/AspNetCore.Docs/blob/master/aspnetcore/grpc/index.md)
* Product: **aspnet-core**
* Technology: **aspnetcore-grpc**
* GitHub Login: @JunTaoLuo
* Microsoft Alias: **johluo**