add comments

Src/AmrCore/AMReX_AmrMesh.cpp

@@ -501,6 +501,9 @@ AmrMesh::ChopGrids (int lev, BoxArray& ba, int target_size) const
  } else {
  IntVect bf(1);
  bf[idim] = rr;
+ // Note that only idim-direction will be chopped by
+ // minmaxSize because the sizes in other directions
+ // are already smaller than chunk.
  ba.minmaxSize(bf, chunk);
  }
  break;