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.
CDR is huge on Riven. You can always purchase more MR, if needed, during the match so I leave most of my glyphs to scale in the direction of giving me the chance to use my abilities as much as possible. The one crit mark isn't necessary. I only have it there because my runes are based off of the Korean player LORD MASTER KING, and, to be honest, that early crit is pretty satisfying if you get it.