doc: fix formatting for README's setup section

[ytvnr]

Just fix the formatting of a section of the README

References

• TODO

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• The PR request is well described and justified, including the body and the references
• The PR title represents the desired changelog entry
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• Test coverage that demonstrates that the change works as expected
• For new features, there's necessary documentation in this pull request or in a subsequent PR to wiremock.org

[RafeArnold]

could these same changes also be made to docs/index.md?

[ytvnr]

@RafeArnold thank you for the review, I just forced push with you suggestions and the update of docs/index.md

[RafeArnold]

thank you very much for the contribution @ytvnr !