How do I save context data to the filesystem?

I added this to the end of my settings.js file and got errors in my log file (of course I didn’t save the error) that pointed me to the line contextStorage: { that “contextStorage” was unknown.

// Save context data to the file-system
  contextStorage: {
      default: {
         module: "localfilesystem"
      }
  }

So, how do I store the context data in a file (to survive a restart)?

Whoops. I forgot to put a comma after the setting above contextStorage.