"Alternatively, you can open the Open3D.sln project with Visual Studio and build the same target." but I am unable to find Open3D.sln

### 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).

### Steps to reproduce the issue

"Alternatively, you can open the Open3D.sln project with Visual Studio and build the same target." but I am unable to find Open3D.sln

### Error message

```shell
"Alternatively, you can open the Open3D.sln project with Visual Studio and build the same target." but I am unable to find Open3D.sln
```

### Open3D, Python and System information

```markdown
- Operating system: Windows 10 64-bit

- Open3D version: 0.15
- System architecture: x64
- Is this a remote workstation?: no
- How did you install Open3D?: build from source
- Compiler version (if built from source): gcc 7.5 / clang 7.0
"Alternatively, you can open the Open3D.sln project with Visual Studio and build the same target." but I am unable to find Open3D.sln
```

### Additional information

"Alternatively, you can open the Open3D.sln project with Visual Studio and build the same target." but I am unable to find Open3D.sln