Update README.md

Author: rofr

README.md

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+## Important notice!
+
+OrigoDB is no longer under active development. Please check out https://github.com/devrexlabs/memstate which is a complete rewrite of OrigoDB with major improvements in the areas performance, availability, licensing, cross-platform, docker and cloud support. Memstate targets .NET Standard 2.0 so will run on .NET Framework >= 4.6.1, .NET Core >= 2.0, Xamarin and Mono.
+
 ## In-memory database for NET/Mono
 
+Looking for .NET Core
+
+
 An Origo database is a command-sourced in-memory object graph.
 
 Write your custom data model, commands and queries using any .NET language, or choose from a number of existing generic models.