docs: mention v1 in readme

[seriousben]

Mentioning the new v1 branch

Fixes #5

[github-actions[bot]]

Previous Coverage	91.7% of statements
New Coverage	91.7% of statements
Patch Coverage	87.0% of changed statements (20/23)

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^{Coverage provided by https://github.com/seriousben/go-patch-cover-action}