Clarify that restarting from a checkpoint requires the same coarse mesh

[stvdwtt]

We recently found out that the coarse mesh defined by the parameters.in file for a simulation restarting from a checkpoint needs to match that of the original simulation. Even a mesh that seems the same when refined, but has a different number of subdivisions won't work.

Example of what won't work (coarse mesh isn't the same): Original run -- 5 refine factor, 2 subdivisions Continuation -- 6 refine factor, 1 subdivision

Example of what will work (coarse mesh is the same): Original run -- 5 refine factor, 1 subdivisions Continuation -- 6 refine factor, 1 subdivision

There should be a note this this effect in the manual.

[david-montiel-t]

Adding a note in the manual. May need to elaborate.