doc: improve unhandledException doc copy

Rework the doc a bit to tighten it up, including removing the
use of `you`

Fix some line wrapping issues.

PR-URL: https://github.com/nodejs/node/pull/5287


Reviewed-By: Roman Klauke <romaaan.git@gmail.com>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>

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