SC-12362 Improve the SonarCloud Intro in README.md

[claire-villard-sonarsource]

List of checkpoint to verify/do before merging a PR.

Dev checklist

• Write/update tests
• Functional validation
• Public documentation update
• Private documentation update
• Clean commits (should start with a ticket number, clear message, no fixup, wip)
• Maximize code coverage as much as possible

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Reviewer checklist

• Code review
• Functional validation
• Check commits are clean

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Steps to validate this PR

Fill-in how you performed the validation, and how the reviewer can replicate it:

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