Remove duplicate reference link in README.md

[yutasb]

Motivation / Background

This Pull Request has been created because the [downloads-badge] reference link was defined twice in README.md (lines 13-14) with identical URLs. According to the Markdown specification, only the first definition is used when multiple definitions exist for the same reference name. The duplicate definition on line 14 serves no purpose and reduces code clarity.

Additional information

Checklist

Before submitting the PR make sure the following are checked:

• This Pull Request is related to one change. Changes that are unrelated should be opened in separate PRs.
• Commit message has a detailed description of what changed and why. If this PR fixes a related issue include it in the commit message. Ex: [Fix #issue-number]
• Tests are added or updated if you fix a bug, refactor something, or add a feature.
• Tests and Rubocop are passing before submitting your proposed changes.

[jremes-foss]

LGTM ✅