Update docs on number of threads and workers in default LocalCluster (#7497)
Update docs on number of threads and workers in default LocalCluster (#7497)

Co-authored-by: cameron16 <28f88066a5690dfb0701a2b38e47157d50652acf@gmail.com>
blaze/dask,dask/dask,dask/dask,jakirkham/dask,blaze/dask,jakirkham/dask