docs: add CONTRIBUTING.md (with associated assets) and CODE_OF_CONDUCT.md

Commit ready for merge.
 - Legacy-Id: 19748

Author: nick

CODE_OF_CONDUCT.md

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+# Code of Conduct
+
+This is a reminder of IETF policies in effect on various topics such as patents
+or code of conduct. It is only meant to point you in the right direction.
+Exceptions may apply. The IETF's patent policy and the definition of an IETF
+"contribution" and "participation" are set forth in
+[BCP 79](https://www.rfc-editor.org/info/bcp79); please read it carefully.
+
+As a reminder:
+ * By participating in the IETF, you agree to follow IETF processes and
+policies.
+ * If you are aware that any IETF contribution is covered by patents or patent
+applications that are owned or controlled by you or your sponsor, you must
+disclose that fact, or not participate in the discussion.
+ * As a participant in or attendee to any IETF activity you acknowledge that
+written, audio, video, and photographic records of meetings may be made public.
+ * Personal information that you provide to IETF will be handled in accordance
+with the IETF Privacy Statement.
+ * As a participant or attendee, you agree to work respectfully with other
+participants; please contact the
+[ombudsteam](https://www.ietf.org/contact/ombudsteam/) if you have questions
+or concerns about this.
+
+Definitive information is in the documents listed below and other IETF BCPs.
+For advice, please talk to WG chairs or ADs:
+
+* [BCP 9 (Internet Standards Process)](https://www.rfc-editor.org/info/bcp9)
+* [BCP 25 (Working Group processes)](https://www.rfc-editor.org/info/bcp25)
+* [BCP 25 (Anti-Harassment Procedures)](https://www.rfc-editor.org/info/bcp25)
+* [BCP 54 (Code of Conduct)](https://www.rfc-editor.org/info/bcp54)
+* [BCP 78 (Copyright)](https://www.rfc-editor.org/info/bcp78)
+* [BCP 79 (Patents, Participation)](https://www.rfc-editor.org/info/bcp79)
+* [Privacy Policy](https://www.ietf.org/privacy-policy/)