Fix syntax issue for relative links in README

[burz]

Description

There was a small issue in the previous PR (#5234) that added a badge displaying the number of GitPOAPs minted for this repository. The issue was that Link References must use square brackets to correctly refer to the referenced link meaning linking like [text][link-ref] as opposed to [text](link-ref) as in other contexts.

You should be able to see that this fixes the issue since it correctly renders now in the preview tab of this PR. My apologies!

Fixes #5356

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• I have selected the correct base branch.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.
• Any dependent changes have been merged and published in downstream modules.
• I ran npm run dtslint with success and extended the tests and types if necessary.
• I ran npm run test:cov and my test cases cover all the lines and branches of the added code.
• I ran npm run build with success.
• I have tested the built dist/web3.min.js in a browser.
• I have tested my code on the live network.
• I have checked the Deploy Preview and it looks correct.
• I have updated the CHANGELOG.md file in the root folder.

Note: I didn't update the CHANGELOG.md as this is a README.md-only change

[Muhammad-Altabba]

Thanks,