docs: readme for dart-folder

dart/README.md

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+## :compass: Dart code for geospatial tools 
+
+**Geospatial** data structures, tools and utilities for 
+[Dart](https://dart.dev/) and [Flutter](https://flutter.dev/) - coordinates,
+geometries, feature objects, metadata, spherical geodesy, projections, tiling
+schemes, vector data models and formats, and geospatial Web APIs.
+
+This folder contains [Dart](https://dart.dev/) code for packages published at 
+[pub.dev](https://pub.dev/publishers/navibyte.com/packages):
+
+Code           | Package | Description 
+-------------- | --------| -----------
+:globe_with_meridians: [geobase](geobase) | [![pub package](https://img.shields.io/pub/v/geobase.svg)](https://pub.dev/packages/geobase) | Geospatial data structures (coordinates, geometries, features, metadata), spherical geodesy, projections and tiling schemes. Vector data format support for [GeoJSON](https://geojson.org/), [WKT](https://en.wikipedia.org/wiki/Well-known_text_representation_of_geometry) and [WKB](https://en.wikipedia.org/wiki/Well-known_text_representation_of_geometry#Well-known_binary).
+:earth_americas: [geodata](geodata) | [![pub package](https://img.shields.io/pub/v/geodata.svg)](https://pub.dev/packages/geodata) | Geospatial feature service Web APIs with support for [GeoJSON](https://geojson.org/) and [OGC API Features](https://ogcapi.ogc.org/features/) clients.
+
+See code and package links above or
+[the repository root](https://github.com/navibyte/geospatial) for more
+information.