[Documentation] Explain exit codes in subsection under debugging section.

[DailyDreaming]

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I think we typically follow LSF-style exit codes on our clusters: https://webcache.googleusercontent.com/search?q=cache:Z-KaimPWsZoJ:https://www.ibm.com/docs/en/SSETD4_9.1.3/lsf_admin/job_exit_codes_lsf.html+&cd=9&hl=en&ct=clnk&gl=us&client=ubuntu

We should clarify these in the docs though. A user just asked what exit code 120 meant in gitter, which is an adjusted exit -9, which is typically a kill by either a user or an out of memory error from the system.

┆Issue is synchronized with this Jira Story ┆Epic: Toil Documentation ┆Issue Number: TOIL-927

[unito-bot]

➤ Adam Novak commented:

We want like a table of Toil exit codes and some explanation of negative exit codes and how they become large positive numbers sometimes.

Also we apparently use a distinct set of exit codes to communicate with LSF.

[unito-bot]

➤ Adam Novak commented:

We could also document exit codes and their signed/unsigned weirdness in general, for people who don’t know their Unix systems programming.