docs: fix Code of Conduct links

[mnebliienko]

Summary

Fix both README and governance links to the organization-owned Code of Conduct. One documentation commit on current main; no protocol or generated-document changes.

Verification

• make -C ietf check passed.
• Full make -C ietf render passed with frozen Ruby dependencies and the existing isolated xml2rfc environment; generated docs are unchanged.
• The consolidated commit has exactly the same tree as the previously reviewed two-commit version.
• GitHub CI still needs maintainer approval of the fork workflow; local validation is not CI.

[mnebliienko]

@nkavian This fork PR has a one-link README fix, but its CI workflow is awaiting maintainer approval and has not run. Could you approve the workflow run when convenient? I will check and address its result afterward.