docs: Update User Guide

[vkhitrin]

Adding exit code documentation.

[github-actions]

🦙 MegaLinter status: ✅ SUCCESS

Descriptor	Linter	Files	Fixed	Errors	Elapsed time
✅ REPOSITORY	checkov	yes		no	12.94s
✅ REPOSITORY	gitleaks	yes		no	0.38s
✅ REPOSITORY	git_diff	yes		no	0.01s
✅ REPOSITORY	grype	yes		no	13.6s
✅ REPOSITORY	secretlint	yes		no	0.74s
✅ REPOSITORY	trivy	yes		no	5.16s
✅ REPOSITORY	trivy-sbom	yes		no	1.11s
✅ REPOSITORY	trufflehog	yes		no	3.86s
✅ RST	rstcheck	1		0	5.85s
✅ RST	rstfmt	1		0	3.28s

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