doc improvement
doc improvement

advanced-programs/concurrentunit,MichaelJY91/concurrentunit,flowersinthesand/concurrentunit,jhalterman/concurrentunit,yodasantu/concurrentunit,jhalterman/concurrentunit,flowersinthesand/concurrentunit,MichaelJY91/concurrentunit,advanced-programs/concurrentunit,yodasantu/concurrentunit