document SimResult and its plot

src/timeresp.jl

@@ -85,6 +85,10 @@ The result structure contains the fields `y, t, x, u` and can be destructured au
 ```julia
 y, t, x, u = result
 ```
+`result::SimResult` can also be plotted directly:
+```julia
+plot(result, plotu=true, plotx=false)
+```
 `y`, `x`, `u` have time in the second dimension. Initial state `x0` defaults to zero.
 
 Continuous time systems are simulated using an ODE solver if `u` is a function. If `u` is an array, the system is discretized (with `method=:zoh` by default) before simulation. For a lower level inteface, see `?Simulator` and `?solve`

src/types/result_types.jl

@@ -3,6 +3,28 @@ abstract type AbstractResult end # Common for all result types, e.g., SimResult
 ## SimResult: the output of lsim etc. ==========================================
 abstract type AbstractSimResult <: AbstractResult end # Result of a time-domain simulation
 
+
+"""
+    SimResult{Ty, Tt, Tx, Tu, Ts} <: AbstractSimResult
+
+Result structure containing the results of time-domain simulations using `lsim, step, impulse`.
+The structure can be plotted using
+```julia
+result = lsim(...)
+plot(result, plotu=true, plotx=false)
+```
+and destructured like
+```julia
+y, t, x, u = result
+```
+
+# Fields:
+- `y::Ty`
+- `t::Tt`
+- `x::Tx`
+- `u::Tu`
+- `sys::Ts`
+"""
 struct SimResult{Ty, Tt, Tx, Tu, Ts} <: AbstractSimResult # Result of lsim
     y::Ty
     t::Tt