clarify that submodules are needed to install
clarify that submodules are needed to install

Fixes #112.
dictav/SwiftLint,sunfei/SwiftLint,lyft/SwiftLint,Johnykutty/SwiftLint,realm/SwiftLint,daniel-beard/SwiftLint,Johnykutty/SwiftLint,realm/SwiftLint,firebase/SwiftLint,jeffreybergier/SwiftLint,eeschimosu/SwiftLint,lyft/SwiftLint,wfleming/SwiftLint,jeffreybergier/SwiftLint,victorpimentel/SwiftLint,sunfei/SwiftLint,daniel-beard/SwiftLint,jeffreybergier/SwiftLint,realm/SwiftLint,Johnykutty/SwiftLint,cdillard/SwiftLint,cdillard/SwiftLint,realm/SwiftLint,victorpimentel/SwiftLint,victorpimentel/SwiftLint,wfleming/SwiftLint,lyft/SwiftLint,lsolniczek/SwiftLint,eeschimosu/SwiftLint,firebase/SwiftLint,victorpimentel/SwiftLint,firebase/SwiftLint,dictav/SwiftLint,firebase/SwiftLint,Johnykutty/SwiftLint,lsolniczek/SwiftLint,lyft/SwiftLint,jeffreybergier/SwiftLint