Add LQG to synthesis docs

Author: baggepinnen

docs/src/lib/synthesis.md

@@ -6,7 +6,7 @@ Pages = ["synthesis.md"]
 
 ```@autodocs
 Modules = [ControlSystems]
-Pages   = ["synthesis.jl", "discrete.jl", "pid_design.jl", "simplification.jl", "connections.jl", "utilities.jl"]
+Pages   = ["synthesis.jl", "discrete.jl", "types/lqg.jl", "pid_design.jl", "simplification.jl", "connections.jl", "utilities.jl"]
 Order   = [:function, :type]
 Private = false
 ```