I tried running the commands under "For example" to enable the grid and it didnt work.
I was very confused and after a lot of messing around I realized I need to run :set grid.
I know it says to run :set grid earlier but I thought it was saying that :set grid can be used (with the addition of the arguments used in the example) to setup a grid.
So I suggest we include :set grid in the example:

For example,
:set grid
:set grid/spacing = 4 4
:set grid/color = #ff0000