OpenFOAM coding training - adding an advection term to our solver and adding a custom class

Topics covered - Add advection operator to laplacianFoam - Examine the effect of advection discretisation approaches - Initial steps at adding a new class for calculating the diffusivity field in our solver (to be finished in the next video at https://youtu.be/zjlTOeJLus4?si=bm9rfp37GKOcyaC1)