Relicense this repository under the Apache v2 and MIT licenses.

* Move licensing information to the top level of the repo.
* Add README.md file with license and contributing info.

LICENSE

@@ -0,0 +1,10 @@
+This component of Racket is distributed under the under the Apache 2.0
+and MIT licenses. The user can choose the license under which they
+will be using the software. There may be other licenses within the
+distribution with which the user must also comply.
+
+See the files
+  https://github.com/racket/racket/blob/master/racket/src/LICENSE-APACHE.txt
+and
+  https://github.com/racket/racket/blob/master/racket/src/LICENSE-MIT.txt
+for the full text of the licenses.

README.md

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+# plot
+
+This the source for the Racket packages: "plot", "plot-compat", "plot-doc", "plot-gui-lib", "plot-lib", "plot-test".
+
+### Contributing
+
+Contribute to Racket by submitting a [pull request], reporting an
+[issue], joining the [development mailing list], or visiting the
+IRC or Slack channels.
+
+### License
+
+Racket, including these packages, is free software, see [LICENSE]
+for more details.
+
+By making a contribution, you are agreeing that your contribution
+is licensed under the [Apache 2.0] license and the [MIT] license.
+
+[MIT]: https://github.com/racket/racket/blob/master/racket/src/LICENSE-MIT.txt
+[Apache 2.0]: https://www.apache.org/licenses/LICENSE-2.0.txt
+[pull request]: https://github.com/racket/plot/pulls
+[issue]: https://github.com/racket/plot/issues
+[development mailing list]: https://lists.racket-lang.org
+[LICENSE]: LICENSE