Fix docs formatting

[JiahaoYao]

this pr fixes the ray build doc issue

reading sources... [100%] ray-more-libs/xgboost-ray
/Users/rliaw/miniconda3/envs/doc/lib/python3.7/site-packages/ray_lightning/ray_ddp.py:docstring of ray_lightning.ray_ddp.RayStrategy:19: WARNING: Unexpected indentation.
/Users/rliaw/miniconda3/envs/doc/lib/python3.7/site-packages/ray_lightning/ray_ddp.py:docstring of ray_lightning.ray_ddp.RayStrategy:21: WARNING: Block quote ends without a blank line; unexpected unindent.
/Users/rliaw/miniconda3/envs/doc/lib/python3.7/site-packages/ray_lightning/ray_ddp.py:docstring of ray_lightning.ray_ddp.RayStrategy:35: WARNING: Error in "code-block" directive:
maximum 1 argument(s) allowed, 38 supplied.

.. code-block:: python
    import pytorch_lightning as ptl
    from ray_lightning import RayAccelerator
    ptl_model = MNISTClassifier(...)
    strategy = RayStrategy(num_workers=4, cpus_per_worker=1,
        use_gpu=True)
    # Don't set ``gpus`` in ``Trainer``.
    # The actual number of GPUs is determined by ``num_workers``.
    trainer = pl.Trainer(..., strategy=strategy)
    trainer.fit(ptl_model)
looking for now-outdated files... none found
pickling environment... done
checking consistency... done
preparing documents... done
writing output... [100%] ray-more-libs/xgboost-ray
/Users/rliaw/ray/doc/source/ray-more-libs/ray-lightning.md:185: WARNING: 'myst' reference target not found: ./docs/horovod_faq.md
generating indices... genindex py-modindex done
lz4 not available, disabling sample compression. This will significantly impact RLlib perf

this is fixed through this pr.

[JiahaoYao]

thank you @amogkam !