add readme.

README.md

@@ -1,14 +1,6 @@
 # argon2_ffi_base
 
-A new Flutter package project.
+only contains the interfaces, which are independent of flutter, so kdbx.dart can
+depend on it, without a dependency on flutter.
 
-## Getting Started
+for flutter use https://github.com/hpoul/argon2_ffi
-
-This project is a starting point for a Dart
-[package](https://flutter.dev/developing-packages/),
-a library module containing code that can be shared easily across
-multiple Flutter or Dart projects.
-
-For help getting started with Flutter, view our 
-[online documentation](https://flutter.dev/docs), which offers tutorials, 
-samples, guidance on mobile development, and a full API reference.