Information matrix: is it rotation first or translation first?

### Checklist

- [X] I have searched for [similar issues](https://github.com/isl-org/Open3D/issues).
- [X] For Python issues, I have tested with the [latest development wheel](http://www.open3d.org/docs/latest/getting_started.html#development-version-pip).
- [X] I have checked the [release documentation](http://www.open3d.org/docs/release/) and the [latest documentation](http://www.open3d.org/docs/latest/) (for `master` branch).

### My Question

Regarding the information matrix:
http://www.open3d.org/docs/release/tutorial/t_pipelines/t_icp_registration.html#Information-Matrix

The documentation only says it's a 6 x 6 matrix but doesn't say anything else. Can the Open3D documentation be updated to clearly indicate if the 6 x 1 Lie algebra parameterization is rotation first or translation first? i.e. is it [rx, ry, rz, tx, ty, tz] or [tx, ty, tz, rx, ry, rz]?