Fix readme minimum nodejs version

[dkrahmer]

Fix install and runtime errors: npm WARN EBADENGINE Unsupported engine { npm WARN EBADENGINE package: '@google/[email protected]', npm WARN EBADENGINE required: { node: '^12.20.0 || ^14.13.1 || >=16.0.0' }, npm WARN EBADENGINE current: { node: 'v12.18.0', npm: '8.15.1' } npm WARN EBADENGINE } npm WARN EBADENGINE Unsupported engine { npm WARN EBADENGINE package: '[email protected]', npm WARN EBADENGINE required: { node: '^12.20.0 || ^14.13.1 || >=16.0.0' }, npm WARN EBADENGINE current: { node: 'v12.18.0', npm: '8.15.1' } npm WARN EBADENGINE } npm WARN EBADENGINE Unsupported engine { npm WARN EBADENGINE package: '[email protected]', npm WARN EBADENGINE required: { node: '^12.20.0 || ^14.13.1 || >=16.0.0' }, npm WARN EBADENGINE current: { node: 'v12.18.0', npm: '8.15.1' } npm WARN EBADENGINE } npm WARN EBADENGINE Unsupported engine { npm WARN EBADENGINE package: '[email protected]', npm WARN EBADENGINE required: { node: '>=12.20' }, npm WARN EBADENGINE current: { node: 'v12.18.0', npm: '8.15.1' } npm WARN EBADENGINE }

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