Can't enable horizontal rulers

How do I enable horizontal rulers so I can see how many characters long each line of code is in a cell? I tried the following in the User Preferences (advanced settings editor) but no rulers show up:

{
    "editorConfig": {
        "rulers": [
            79
        ]
    }
}

It looks like you changed the Text Editor advanced config. To change the notebook cell editors, you’ll need to go to the Notebook advanced config and configure those editors separately with something like:

{
    codeCellConfig: {
        rulers: [80],
    },
    markdownCellConfig: {
        rulers: [80],
    }
}