doc: mention triage in GOVERNANCE.md

Refs: https://github.com/nodejs/node/pull/34295#issuecomment-660495710
PR-URL: https://github.com/nodejs/node/pull/34426


Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Michael Dawson <Michael_Dawson@ca.ibm.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>