add docs on chunks choice
add docs on chunks choice

dask/dask,jakirkham/dask,cpcloud/dask,mrocklin/dask,cowlicks/dask,mraspaud/dask,ContinuumIO/dask,mraspaud/dask,ContinuumIO/dask,jcrist/dask,jakirkham/dask,blaze/dask,dask/dask,chrisbarber/dask,jcrist/dask,gameduell/dask,mikegraham/dask,blaze/dask,mrocklin/dask