Add subcommand to windows install instructions
Add subcommand to windows install instructions

As written, windows ninja-based build and install instructions successfully build gRPC, but do not install anything. Additionally, the last line of the instructions does nothing, because it duplicates the effect of the next-to-last-line. Adding "install" to the last line fixes both issues.
dgquintas/grpc,ejona86/grpc,chrisdunelm/grpc,carl-mastrangelo/grpc,grpc/grpc,jtattermusch/grpc,dgquintas/grpc,dgquintas/grpc,grpc/grpc,simonkuang/grpc,ncteisen/grpc,stanley-cheung/grpc,stanley-cheung/grpc,stanley-cheung/grpc,firebase/grpc,stanley-cheung/grpc,thinkerou/grpc,jboeuf/grpc,vjpai/grpc,mehrdada/grpc,ejona86/grpc,ncteisen/grpc,mehrdada/grpc,stanley-cheung/grpc,sreecha/grpc,ncteisen/grpc,muxi/grpc,dgquintas/grpc,jboeuf/grpc,jtattermusch/grpc,Vizerai/grpc,Vizerai/grpc,muxi/grpc,ctiller/grpc,grpc/grpc,vjpai/grpc,sreecha/grpc,jtattermusch/grpc,muxi/grpc,dgquintas/grpc,ejona86/grpc,grpc/grpc,ctiller/grpc,dgquintas/grpc,sreecha/grpc,firebase/grpc,ctiller/grpc,muxi/grpc,Vizerai/grpc,carl-mastrangelo/grpc,kpayson64/grpc,donnadionne/grpc,mehrdada/grpc,vjpai/grpc,stanley-cheung/grpc,ejona86/grpc,carl-mastrangelo/grpc,carl-mastrangelo/grpc,nicolasnoble/grpc,ctiller/grpc,vjpai/grpc,nicolasnoble/grpc,ncteisen/grpc,ctiller/grpc,pszemus/grpc,nicolasnoble/grpc,jboeuf/grpc,simonkuang/grpc,jtattermusch/grpc,stanley-cheung/grpc,firebase/grpc,vjpai/grpc,vjpai/grpc,ejona86/grpc,donnadionne/grpc,Vizerai/grpc,ejona86/grpc,vjpai/grpc,mehrdada/grpc,simonkuang/grpc,jtattermusch/grpc,thinkerou/grpc,pszemus/grpc,donnadionne/grpc,vjpai/grpc,sreecha/grpc,ejona86/grpc,pszemus/grpc,vjpai/grpc,Vizerai/grpc,thinkerou/grpc,dgquintas/grpc,chrisdunelm/grpc,jboeuf/grpc,simonkuang/grpc,carl-mastrangelo/grpc,thinkerou/grpc,thinkerou/grpc,jboeuf/grpc,ctiller/grpc,mehrdada/grpc,jtattermusch/grpc,kpayson64/grpc,stanley-cheung/grpc,grpc/grpc,jboeuf/grpc,Vizerai/grpc,jtattermusch/grpc,ctiller/grpc,simonkuang/grpc,donnadionne/grpc,ncteisen/grpc,ncteisen/grpc,donnadionne/grpc,firebase/grpc,jboeuf/grpc,firebase/grpc,firebase/grpc,ejona86/grpc,ncteisen/grpc,grpc/grpc,kpayson64/grpc,donnadionne/grpc,Vizerai/grpc,dgquintas/grpc,carl-mastrangelo/grpc,jtattermusch/grpc,carl-mastrangelo/grpc,muxi/grpc,mehrdada/grpc,jtattermusch/grpc,mehrdada/grpc,kpayson64/grpc,kpayson64/grpc,chrisdunelm/grpc,ncteisen/grpc,kpayson64/grpc,nicolasnoble/grpc,jboeuf/grpc,nicolasnoble/grpc,Vizerai/grpc,muxi/grpc,carl-mastrangelo/grpc,grpc/grpc,thinkerou/grpc,carl-mastrangelo/grpc,grpc/grpc,vjpai/grpc,firebase/grpc,jtattermusch/grpc,thinkerou/grpc,grpc/grpc,grpc/grpc,stanley-cheung/grpc,donnadionne/grpc,jtattermusch/grpc,jboeuf/grpc,nicolasnoble/grpc,chrisdunelm/grpc,thinkerou/grpc,chrisdunelm/grpc,donnadionne/grpc,ncteisen/grpc,ctiller/grpc,chrisdunelm/grpc,donnadionne/grpc,ncteisen/grpc,Vizerai/grpc,carl-mastrangelo/grpc,mehrdada/grpc,chrisdunelm/grpc,Vizerai/grpc,ejona86/grpc,donnadionne/grpc,pszemus/grpc,chrisdunelm/grpc,sreecha/grpc,stanley-cheung/grpc,nicolasnoble/grpc,vjpai/grpc,sreecha/grpc,simonkuang/grpc,kpayson64/grpc,grpc/grpc,dgquintas/grpc,pszemus/grpc,ejona86/grpc,simonkuang/grpc,nicolasnoble/grpc,chrisdunelm/grpc,carl-mastrangelo/grpc,chrisdunelm/grpc,thinkerou/grpc,muxi/grpc,mehrdada/grpc,sreecha/grpc,muxi/grpc,donnadionne/grpc,stanley-cheung/grpc,grpc/grpc,thinkerou/grpc,pszemus/grpc,sreecha/grpc,sreecha/grpc,jboeuf/grpc,pszemus/grpc,chrisdunelm/grpc,ctiller/grpc,pszemus/grpc,nicolasnoble/grpc,dgquintas/grpc,mehrdada/grpc,jboeuf/grpc,mehrdada/grpc,sreecha/grpc,kpayson64/grpc,nicolasnoble/grpc,simonkuang/grpc,nicolasnoble/grpc,ncteisen/grpc,mehrdada/grpc,pszemus/grpc,sreecha/grpc,Vizerai/grpc,muxi/grpc,jboeuf/grpc,kpayson64/grpc,vjpai/grpc,sreecha/grpc,firebase/grpc,simonkuang/grpc,ctiller/grpc,dgquintas/grpc,firebase/grpc,thinkerou/grpc,kpayson64/grpc,muxi/grpc,jtattermusch/grpc,thinkerou/grpc,firebase/grpc,firebase/grpc,stanley-cheung/grpc,kpayson64/grpc,ejona86/grpc,muxi/grpc,ncteisen/grpc,muxi/grpc,ctiller/grpc,carl-mastrangelo/grpc,ejona86/grpc,pszemus/grpc,donnadionne/grpc,pszemus/grpc,pszemus/grpc,nicolasnoble/grpc,firebase/grpc,ctiller/grpc