Add a simple README and Contributing.md.

Author: sunfishcode

Contributing.md

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+# Contributing to WebAssembly
+
+Interested in participating? Please follow
+[the same contributing guidelines as the design repository][].
+
+  [the same contributing guidelines as the design repository]: https://github.com/WebAssembly/design/blob/master/Contributing.md
+
+Also, please be sure to read [the README.md](README.md) for this repository.

README.md

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+# WebAssembly System Interface
+
+![WASI](WASI.png)
+
+This repository accompanies the WebAssembly WASI Subgroup,
+focused on the design of the WASI, the WebAssembly System Interface.
+
+We'll be adding more content here, but for now, check out these:
+ - https://hacks.mozilla.org/2019/03/standardizing-wasi-a-webassembly-system-interface/ - Blog post introducing WASI
+ - https://wasi.dev/ - Links to more information about WASI
+ - https://github.com/WebAssembly/WASI/issues - This repo's issue tracker
+
+The issue tracker is the place to ask questions, make suggestions, and start
+discussions.
+
+As a W3C CG Subgroup, we'll also be having meetings. Once we have a schedule
+for those, we'll post that here also.