pandas.read_parquet with parallel reads using pyarrow nthreads
According to these sources, `pyarrow.parquet` supports an `nthreads` argument for parallel reads, i.e.
- https://wesmckinney.com/blog/python-parquet-multithreading/ the pyarrow.parquet engine
- https://arrow.apache.org/docs/python/parquet.html#multithreaded-reads

```python
import pyarrow.parquet as pq
table = pq.read_table(file_path, nthreads=4)
```

The `nthreads=4` argument raises an exception in `pandas.read_parquet` rather than passing the argument through to the `pyarrow.parquet` engine.  The pandas documentation indicates the `**kwargs` are passed to the parquet engine (`pyarrow` in this case), e.g.

```python
import pandas as pd
import pyarrow.parquet

pd.read_parquet(
            parquet_path, engine="pyarrow", columns=query_columns, nthreads=6
        )
```

```versions
$ cat /etc/lsb-release 
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=18.04
DISTRIB_CODENAME=bionic
DISTRIB_DESCRIPTION="Ubuntu 18.04.2 LTS"

$ pip freeze | grep pandas
geopandas==0.4.1
pandas==0.24.2

$ pip freeze | grep pyarrow
pyarrow==0.13.0
```

```text
Traceback (most recent call last):
  File "./poc/hazard_to_parquet.py", line 128, in <module>
    convert()
  File "/home/joe/miniconda3/envs/proj/lib/python3.7/site-packages/click/core.py", line 764, in __call__
    return self.main(*args, **kwargs)
  File "/home/joe/miniconda3/envs/proj/lib/python3.7/site-packages/click/core.py", line 717, in main
    rv = self.invoke(ctx)
  File "/home/joe/miniconda3/envs/proj/lib/python3.7/site-packages/click/core.py", line 956, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/home/joe/miniconda3/envs/proj/lib/python3.7/site-packages/click/core.py", line 555, in invoke
    return callback(*args, **kwargs)
  File "./poc/hazard_to_parquet.py", line 114, in convert
    parquet_path, engine="pyarrow", columns=query_columns, nthreads=6
  File "/home/joe/miniconda3/envs/proj/lib/python3.7/site-packages/pandas/io/parquet.py", line 282, in read_parquet
    return impl.read(path, columns=columns, **kwargs)
  File "/home/joe/miniconda3/envs/proj/lib/python3.7/site-packages/pandas/io/parquet.py", line 129, in read
    **kwargs).to_pandas()
TypeError: read_table() got an unexpected keyword argument 'nthreads'
```