docs: Include documentation about using `set -x` for troubleshooting modules

[fiftydinar]

In this case, set -euxo pipefail.

It is very useful for watching what module does command by command & potentially seeing where it silently fails.

Some commands like find can show this behavior with errors similar to this:

find: paths must precede expression: `'

[fiftydinar]

This is implemented in WIP bash module code guidelines, so I'll close this as completed.