Suggestion for "using the grid" documentation section.

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
```