Update governance.rst to mention NumFocus CoC

Author: apdavison

doc/source/governance.rst

@@ -5,7 +5,8 @@ Governance
 Neo is a community-developed project,
 we welcome contributions from anyone who is interested in the project.
 The project maintainers are the members of the `Neo maintainers team`_.
-All contributors agree to abide by the Code of Conduct, see the file `CODE_OF_CONDUCT.md`_.
+All contributors agree to abide by the [NumFocus Code of Conduct](https://numfocus.org/code-of-conduct),
+see the file `CODE_OF_CONDUCT.md`_.
 
 Contributions
 =============