docs: more sphinx errors.

No errors locally but gh actions doesn't like it.
Plus US spelling

Author: lachlangrose

docs/source/user_guide/visualisation.rst

@@ -56,6 +56,7 @@ The default behaviour of the viewer can also be modified.
 To change the resolution of the scalar field or isosurfacing, either set the number of steps in x,y,z or the total number of elements of tht bounding box
 
 .. code-block::
+    
     model.bounding_box.nsteps = np.array([nx,ny,nz])
     print(model.bounding_box.nsteps)
     model.bounding_box.nelements = 1e6

docs/source/user_guide/what_is_a_geological_model.rst

@@ -121,8 +121,8 @@ If we were to change the length of the vector we would change the distance betwe
     mesh2 = bounding_box.structured_grid()
     mesh2.properties['val'] = interpolator.evaluate_value(mesh2.nodes)
     view = Loop3DView()
-    view.add_mesh(mesh2.vtk().contour([-1, 0, 1]),colour='red')
-    view.add_mesh(mesh.vtk().contour([-1, 0, 1]),colour='blue')
+    view.add_mesh(mesh2.vtk().contour([-1, 0, 1]),color='red')
+    view.add_mesh(mesh.vtk().contour([-1, 0, 1]),color='blue')
     view.add_points(data[["X", "Y", "Z"]].values)
     view.add_arrows(
         vector[["X", "Y", "Z"]].values,