doc: suggest not to throw JS errors from C++

Also provide an example on how to use internal/errors to handle errors in C++.

Refs: https://github.com/nodejs/node/issues/18106

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

doc