doc: fix doc for napi_get_typedarray_info
The data pointer returned for the typedarray has already been adjusted by the offset so it does not point to the start of the buffer, instead id points to the start of the first element.
I think we probably would have liked it to point to the start of the buffer, but we can't change as that would be a breaking change.
Update the doc to match the implementation.
Fixes: https://github.com/nodejs/node-addon-api/issues/244
Checklist
- [X ]
make -j4 test
(UNIX), orvcbuild test
(Windows) passes .- [X] documentation is changed or added -
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