Add more plots to vorticity example

When I initially coded the vorticity-based Navier-Stokes [simulation](https://algebraicjulia.github.io/Decapodes.jl/dev/navier_stokes/ns/), I created plots that emulate those from the [reference paper](https://arxiv.org/abs/1508.01166) from Mohamed et al.

For demonstration purposes, the (a) vector-field corresponding to the vorticity plot should also be displayed.