added docs for backfill and reschedule
added docs for backfill and reschedule

treasure-data/digdag,KimuraTakaumi/digdag,treasure-data/digdag,treasure-data/digdag,KimuraTakaumi/digdag,KimuraTakaumi/digdag,treasure-data/digdag,KimuraTakaumi/digdag,treasure-data/digdag,KimuraTakaumi/digdag,KimuraTakaumi/digdag,treasure-data/digdag,treasure-data/digdag