Separates the last section with subheading

docs/src/tutorials/parameter_estimation.md

@@ -88,9 +88,10 @@ plot!(sol_estimate,color=[:darkblue :darkred], linestyle=:dash,lw=3,label=["X es
 ```
 ![parameter_estimation_plot4](../assets/parameter_estimation_plot4.svg)
 
-The final parameter set becomes `[0.9996559014056948, 2.005632696191224]` (the real one was [1.0, 2.0]`).
+The final parameter set becomes `[0.9996559014056948, 2.005632696191224]` (the real one was `[1.0, 2.0]`).
 
 
+### Why we fit the parameters in iterations.
 The reason we chose to fit the model on a smaller interval to begin with, and then extend the interval, is to avoid getting stuck in a local minimum. Here specifically, we chose our initial interval to be smaller than a full cycle of the oscillation. If we had chosen to fit a parameter set on the full interval immediately we would have received an inferior solution.
 ```julia
 p_estimate = optimise_p([5.,5.],30.).minimizer