Document #4772, and at the same time heavily edit the section describing concurrency limits.
Document #4772, and at the same time heavily edit the section describing
concurrency limits.

neurodebian/htcondor,neurodebian/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,neurodebian/htcondor,htcondor/htcondor,neurodebian/htcondor,neurodebian/htcondor,htcondor/htcondor,neurodebian/htcondor,neurodebian/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,neurodebian/htcondor,neurodebian/htcondor