Link retail POS returns and refunds checklist

[sridharkalaibala]

What does this PR do?

Adds the published retail POS returns, refunds, and voids checklist to the README resource table.

The vendor-neutral guide covers original-sale verification, approvals, payment reversals, inventory disposition, Offline POS controls, Online/Offline POS synchronization, reconciliation, and retained evidence. It links the canonical website at https://www.posnic.com/ and the public source at https://github.com/Posnic/POS.

Acceptance criteria covered

• Adds one focused, live retail-operations resource
• Uses factual POS and Billing Software language
• Preserves the canonical website and source targets

How was it tested?

• node --test tests/docs-links.test.js (2 passed)
• git diff --check
• Live guide returned HTTP 200
• Pages and IndexNow workflows succeeded
• Live page uses the canonical website https://www.posnic.com/

Checklist

• One focused change
• Commit is signed off (DCO)
• Documentation-only; no runtime behavior changes
• Matches the existing README resource-table format

Disclosure

I am affiliated with Posnic. OpenAI Codex assisted with preparing and validating this documentation contribution. The linked guide is first-party content and is not presented as an independent endorsement.

[github-actions]

Merged to develop. Anyone can test this - you do not need write access.

Try it at https://develop.posnic.io, or run it yourself:

git fetch origin develop && git checkout develop
npm install && npm --prefix api install
npm run dev   # then http://localhost:3000

When you have tested it, say what you did and what happened, and set
QA passed or QA failed. If you cannot set labels, just comment -
a maintainer will.

Reporting that something is broken is as useful as fixing it. It is
better found here than by a shopkeeper.