Clarify the connection between subprocesses and --concurrency
Clarify the connection between subprocesses and --concurrency

nedbat/coveragepy,hugovk/coveragepy,nedbat/coveragepy,nedbat/coveragepy,hugovk/coveragepy,hugovk/coveragepy,hugovk/coveragepy,hugovk/coveragepy,nedbat/coveragepy,nedbat/coveragepy