Update README.md

Author: tsimbalar

README.md

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 # SerilogWeb.Classic.Mvc [![Build status](https://ci.appveyor.com/api/projects/status/3yidmjq6pm0f2pii?svg=true)](https://ci.appveyor.com/project/serilog-web/classic-mvc)
 
+>  **Deprecation notice:** this package is no longer maintained. The world has moved on to ASP.NET Core. Take a look at [Serilog.AspNetCore](https://github.com/serilog/serilog-aspnetcore) instead!
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 ASP.NET MVC support for [SerilogWeb.Classic](https://github.com/serilog-web/classic).
 
 *Package* - <a href="https://www.nuget.org/packages/serilogweb.classic.mvc">SerilogWeb.Classic.Mvc</a> | Platforms - .NET 4.5