github: add foundation templates

Standard templates for foundation repos for code of conduct and
contribution guidelines. The latter can be extended if needed.

Signed-off-by: Gerwin Klein <gerwin.klein@proofcraft.systems>

.github/CODE_OF_CONDUCT.md

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+<!--
+     Copyright 2020, Data61, CSIRO (ABN 41 687 119 230)
+
+     SPDX-License-Identifier: CC-BY-SA-4.0
+-->
+
+# Code of Conduct
+
+This repository and interactions with it fall under the [seL4 Code of Conduct][1] available from the [seL4 website][2].
+
+[1]: https://docs.sel4.systems/processes/conduct.html
+[2]: https://sel4.systems

.github/CONTRIBUTING.md

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+<!--
+     Copyright 2020, Data61, CSIRO (ABN 41 687 119 230)
+
+     SPDX-License-Identifier: CC-BY-SA-4.0
+-->
+
+# Contributions Welcome
+
+Please see the [seL4 contributing guidelines][1] on the [seL4 website][2] for
+details.
+
+[1]: https://docs.sel4.systems/processes/contributing.html
+[2]: https://sel4.systems
+
+
+## Contact
+
+If you have larger changes or additions, it is a good idea to get in contact
+with us as <devel@sel4.systems>, so we can help you get started.
+
+The people responsible for the technical direction, procedures, and quality
+control are the [Technical Steering Committee][3] (TSC) of the seL4
+foundation. You can contact them either on the developer mailing list or on
+directly via email available from their profile pages.
+
+[3]: https://sel4.systems/Foundation/TSC
+
+
+## Developer Certificate of Origin (DCO)
+
+This repository uses the same sign-off process as the Linux kernel. For every
+commit, use
+
+    git commit -s
+
+to add a sign-off line to your commit message, which will come out as:
+
+    Signed-off-by: name <email>
+
+By adding this line, you make the declaration that you have the right to make
+this contribution under the open source license the files use that you changed
+or contributed.
+
+The full text of the declaration is at <https://developercertificate.org>.