add docstrings to progress
add docstrings to progress

dask/distributed,amosonn/distributed,dask/distributed,mrocklin/distributed,broxtronix/distributed,mrocklin/distributed,blaze/distributed,dask/distributed,amosonn/distributed,amosonn/distributed,broxtronix/distributed,blaze/distributed,mrocklin/distributed,dask/distributed,broxtronix/distributed