This PR adds documentation of models supported by the `Unstructured`
tool. The changes reflect the tool's capabilities, usage examples, and
the process for integrating custom models.
Sections:
- Detailed the basic usage of the `Unstructured` partition with the
model name.
- Provided a list of available models in the `Unstructured` partition.
- Added instructions on using non-default models via three distinct
methods.
- Explained leveraging models from the LayoutParser's model zoo with
`UnstructuredDetectronModel`.
- Guided users in integrating their custom object detection models using
the `UnstructuredObjectDetectionModel` class.
Tested the docs build with:
> cd docs
> pip install -r requirements.txt
> make html
