Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
So in general: You get so much movement speed thx to your Passive, Black Cleaver, Statix, Phantom Dancer, Boots of Swiftness. You also gain Armor penetrtion what works great with your q and w. You also gain crit and attackspeed you really need. You can also buy Infinty Edge very after Black Cleaver to get more damage output but Black Cleaver is the core item. The stats it gives you for so less gold is very good. On Lucian you can see it works very great too or even better but sivir does well with it too. You can choose your own Runes and masteries but with this attack speed and crit you will make much mor damage thx to Fervor for Battle. I do max e the second because you need your spellshield up more often. But you can also max w secound if you prefer this. Try it out ^^ its funny running away from a riven when you do not have boots but still getting away cause of your movementspeed and e (and r and teammates but those are rare situations) I am sorry for any language mistakes but, hey, i tried