Fix 549 docs on user defined output path

[nesnoj]

Summary of the discussion

Re-adds instructions how to use env vars to docs.

Type of change (CHANGELOG.md)

Updated

• Fix docs on user-defined output path for csv, xml, database #549

Workflow checklist

Automation

Closes #549

PR-Assignee

• [x] 🐙 Follow the workflow in CONTRIBUTING.md
• [x] 📝 Update the CHANGELOG.md
• [x] 📙 Update the documentation

Reviewer

• [ ] 🐙 Follow the Reviewer Guidelines
• [ ] 🐙 Provided feedback and show sufficient appreciation for the work done