meta: move the Code of Conduct to TSC repository

PR-URL: https://github.com/nodejs/node/pull/12147
Ref: https://github.com/nodejs/TSC/issues/224
Ref: https://github.com/nodejs/TSC/pull/232


Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>