docs: add tested rsynchl quickstart

[Suryansh-FSD]

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[Suryansh-FSD]

Summary

Adds a practical rsynchl example to the quickstart documentation.

The new section:

• shows the expected snapshot-directory structure;
• demonstrates repository initialization and import commands;
• explains archive naming and timestamps;
• shows how to verify imported archives;
• documents temporary snapshot renaming and safety precautions.

This contributes toward borg-import issue #16 and borgbackup/borg#4426.

Verification

Tested end to end using Borg 1.4.5 and the current borg-import master branch. Two snapshot directories sharing a hard-linked file were imported successfully.

• Both archives appeared in borg list --short.
• The original snapshot directories remained unchanged.
• pytest -q: 6 passed
• flake8 src: passed
• black --check src: passed
• Sphinx HTML documentation build: passed