Where to send when something is missing or wrong in documentation ?

### 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

Drawing does not show in firefox or chrome in page :
documentation 0.15.1
http://www.open3d.org/docs/release/tutorial/geometry/kdtree.html

Where should we post such issues as a feedback ?