sequences: update docs a bit
sequences: update docs a bit

dch/factor,AlexIljin/factor,bjourne/factor,sarvex/factor-lang,bpollack/factor,bjourne/factor,mrjbq7/factor,sarvex/factor-lang,dch/factor,slavapestov/factor,dch/factor,tgunr/factor,slavapestov/factor,dch/factor,slavapestov/factor,bpollack/factor,slavapestov/factor,nicolas-p/factor,bjourne/factor,tgunr/factor,dch/factor,bpollack/factor,nicolas-p/factor,bpollack/factor,slavapestov/factor,nicolas-p/factor,tgunr/factor,sarvex/factor-lang,tgunr/factor,factor/factor,factor/factor,AlexIljin/factor,bpollack/factor,sarvex/factor-lang,tgunr/factor,AlexIljin/factor,nicolas-p/factor,mrjbq7/factor,nicolas-p/factor,slavapestov/factor,factor/factor,factor/factor,bpollack/factor,AlexIljin/factor,nicolas-p/factor,mrjbq7/factor,slavapestov/factor,tgunr/factor,dch/factor,sarvex/factor-lang,mrjbq7/factor,sarvex/factor-lang,nicolas-p/factor,sarvex/factor-lang,bjourne/factor,factor/factor,bpollack/factor,mrjbq7/factor,AlexIljin/factor,AlexIljin/factor,bjourne/factor,AlexIljin/factor,bjourne/factor,mrjbq7/factor,bjourne/factor,factor/factor