DOC: Update 'Go Reference' badge in README.md to v2 documentation

[mrngm]

This PR points the 'Go reference' badge in the README to the v2 documentation on pkg.go.dev.

Description

• Bug fix
• Feature addition
• Code refactoring
• Documentation update
• Other (please explain):

How Has This Been Tested?

• Unit tests
• Integration tests
• Manual testing

Checklist

• My code follows the style guidelines of this project.
• I have performed a self-review of my code.
• I have made corresponding changes to the documentation.
• I have added tests that ensure my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.
• Any dependent changes have been merged and published in downstream modules.

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