Update README.md

[rajsite]

The example snippet in the README shows the @geoarrow/geoarrow-js/worker entrypoint but the rollup and src/index.ts config show a worker named import instead. This updates the README to reflect that difference.

[rajsite]

@kylebarron This PR fixes the imports of the README example, but it looks like the README example still has other issues, see: #25

[kylebarron]

I'm not really sure which is the better import; JS bundling confuses me.

As for the example, as a quick fix to have a working example, we can switch to

const originalData = arrow.makeVector(new Int32Array([1, 2, 3])).data[0];