Update guide to mention correct subdirectory
Update guide to mention correct subdirectory

The guide as written results in lots of repositories being placed as siblings to `swift-project`, instead of inside of it. This also results in the `build` directory being a sibling. Changing the clone to the `swift` directory fixes this.

tkremenek/swift,rudkx/swift,parkera/swift,xwu/swift,JGiola/swift,ahoppen/swift,rudkx/swift,apple/swift,gregomni/swift,atrick/swift,rudkx/swift,apple/swift,tkremenek/swift,JGiola/swift,benlangmuir/swift,roambotics/swift,glessard/swift,atrick/swift,parkera/swift,benlangmuir/swift,tkremenek/swift,benlangmuir/swift,glessard/swift,ahoppen/swift,tkremenek/swift,rudkx/swift,xwu/swift,apple/swift,hooman/swift,glessard/swift,parkera/swift,apple/swift,parkera/swift,hooman/swift,JGiola/swift,glessard/swift,tkremenek/swift,hooman/swift,gregomni/swift,glessard/swift,tkremenek/swift,JGiola/swift,parkera/swift,atrick/swift,apple/swift,atrick/swift,roambotics/swift,parkera/swift,ahoppen/swift,roambotics/swift,hooman/swift,JGiola/swift,rudkx/swift,gregomni/swift,parkera/swift,benlangmuir/swift,benlangmuir/swift,apple/swift,ahoppen/swift,hooman/swift,ahoppen/swift,gregomni/swift,rudkx/swift,tkremenek/swift,ahoppen/swift,xwu/swift,benlangmuir/swift,parkera/swift,xwu/swift,xwu/swift,atrick/swift,roambotics/swift,roambotics/swift,xwu/swift,gregomni/swift,JGiola/swift,xwu/swift,hooman/swift,hooman/swift,glessard/swift,atrick/swift,roambotics/swift,gregomni/swift