don't attempt to save graph (documenter cannot handle)

Author: TorkelE

docs/src/model_creation/model_visualisation.md

@@ -63,10 +63,9 @@ nothing # hide
 !["Repressilator Graph"](../assets/network_graphs/repressilator_graph.png)
 
 A generated graph can be saved using the `savegraph` function:
-```@example visualisation_graphs
+```julia
 repressilator_graph = Graph(repressilator)
 savegraph(repressilator_graph, "repressilator_graph.png")
-rm("repressilator_graph.png") # hide
 ```
 
 Finally, a [network's reaction complexes](@ref network_analysis_reaction_complexes) (and the reactions in between these) can be displayed using the `complexgraph(brusselator)` function:
@@ -75,4 +74,4 @@ complexgraph(brusselator)
 nothing # hide
 ```
 !["Repressilator Complex Graph"](../assets/network_graphs/repressilator_complex_graph.png)
-Here, reaction complexes are displayed as blue nodes, and reactions in between these as black arrows.
+Here, reaction complexes are displayed as blue nodes, and reactions in between these as black arrows.