Update README.md

Author: nblumhardt

README.md

@@ -15,7 +15,7 @@ A simple `Hello, {User}` event.
 Install from [NuGet](https://nuget.org/packages/Serilog.Formatting.Compact):
 
 ```powershell
-Install-Package Serilog.Formatting.Compact
+Install-Package Serilog.Formatting.Compact -Pre
 ```
 
 The formatter is used in conjunction with sinks that accept `ITextFormatter`. For example, the [rolling file](https://github.com/serilog/serilog-sinks-rollingfile) sink: