doc: expand C++ README with information about exception handling

Add more information about why it is advisable not to use
`.FromJust()` etc. on Maybe(Local)s, and general information
about termination exceptions.

PR-URL: https://github.com/nodejs/node/pull/31720


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Sam Roberts <vieuxtech@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Denys Otrishko <shishugi@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>