doc: adds assert doc for strict mode with pointer to strict equality

Refs: https://github.com/nodejs/node/issues/30485

PR-URL: https://github.com/nodejs/node/pull/30486


Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>