Add documentation for the dart official image (#1944)

dart/README-short.txt

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+Dart is a client-optimized language for fast apps on any platform.

dart/content.md

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+# What is Dart?
+
+Dart is a client-optimized language for developing fast apps on any platform. Its goal is to offer the most productive programming language for multi-platform development, paired with a flexible execution runtime platform for app frameworks. For more details, see https://dart.dev.
+
+By utilizing Dart's support for ahead-of-time (AOT) [compilation to executables](https://dart.dev/tools/dart-compile#exe), you can create very small runtime images (~10 MB).
+
+%%LOGO%%
+
+## Using this image
+
+We recommend creating small runtime images by leveraging Dart's support for ahead-of-time (AOT) [compilation to executables](https://dart.dev/tools/dart-compile#exe). This enables creating small runtime images (~10 MB).
+
+The following `Dockerfile` performs two steps:
+
+1.	Using the Dart SDK in the `dart:stable` image, compiles your server (`bin/server.dart`) to an executable (`server`).
+
+2.	Assembles the runtime image by combining the compiled server with the Dart VM runtime and it's needed dependencies located in `/runtime/`.
+
+```Dockerfile
+# Specify the Dart SDK base image version using dart:<version> (ex: dart:2.12)
+FROM dart:stable AS build
+
+# Resolve app dependencies.
+WORKDIR /app
+COPY pubspec.* .
+RUN dart pub get
+
+# Copy app source code and AOT compile it.
+COPY . .
+RUN dart compile exe bin/server.dart -o /server
+
+# Build minimal serving image from AOT-compiled `/server` and required system
+# libraries and configuration files stored in `/runtime/` from the build stage.
+FROM scratch
+COPY --from=build /runtime/ /
+COPY --from=build /server /bin/
+
+# Start server.
+EXPOSE 8080
+CMD ["/bin/server"]
+```
+
+If you have [Docker Desktop](https://www.docker.com/get-started) installed, you can build and run on your machine with the `docker` command:
+
+```shell
+$ docker build -t dart-server .
+$ docker run -it --rm -p 8080:8080 --name myserver dart-server
+```
+
+When finished, you can stop the container using the name you provided:
+
+```shell
+$ docker kill myserver
+```
+
+Maintained with ❤️ by the [Dart](https://dart.dev) team.

dart/github-repo

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+https:/github.com/dart-lang/dart-docker

dart/license.md

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+View [license information](https://github.com/dart-lang/sdk/blob/master/LICENSE) for the software contained in this image.

dart/maintainer.md

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+The Dart Docker Team