Instructions for shorcut editor is out of date

[plynch-chwy]

The instructions for editing user shortcuts seem to be out of date (Version 1.2.3).

In the system defaults shortcuts, there is an example comment for how to disable a keyboard shortcut:

    // Note: To disable a system default shortcut,
    // copy it to User Preferences and add the
    // "disabled" key, for example:
    // {
    //     "command": "application:activate-next-tab",
    //     "keys": [
    //         "Ctrl Shift ]"
    //     ],
    //     "selector": "body",
    //     "disabled": true
    // }

The stable docs also has a short video on how to change a keyboard shortcut:
https://jupyterlab.readthedocs.io/en/stable/user/interface.html#keyboard-shortcuts
https://www.youtube.com/watch?v=rhW3kAExCik

These instructions seem to be out of date and don't match current json structure of system defaults.

For me to add a shortcut I had to use this structure (which isn't immediately obvious since the User Preferences starts as {}):

{
    "shortcuts": [
        {
            "command": "apputils:activate-command-palette",
            "keys": [
                "Accel Shift P"
            ],
            "selector": "body"
        }
    ]
}

May be more helpful to set the default User Preferences to something that makes it easier for new users to copy and paste the current shortcuts into their preferences like below:

{
    "shortcuts": [
    ]
}

[groutr]

I also ran into this working on #7589. @plynch-chwy, that is a good suggestion, however, #7597 would remove the need to edit a settings file altogether. You're right, though, the documentation is out of date.