Add $schema to schema

Adding the “$schema” prop would allow IDE support for IntelliSense.

One can add it to the config file themselves, but then IDE throws a little warning that “Property $schema is not allowed.” Not a big deal, but it’d be nice to do away without the warning.

{
  "$schema": "./node_modules/markdownlint/schema/markdownlint-config-schema.json",
  "default": true,
  "MD013": {
    "line_length": 100
  }
}

[DavidAnson]

Thanks. This should be fine to add.

[moltar]

Maybe it’s just VS Code specific, but it is documented here, and I can confirm it works.

https://code.visualstudio.com/docs/languages/json#_json-schemas-and-settings

Even without the markdownlint VS Code extension, I get IntelliSense.

Here’s a video demo of that: https://drive.google.com/file/d/14TvQkNnwSFo80upePXA-oUudln-qIWMP/view?usp=drivesdk

I renamed $schema to _$schema first to disable the behavior, which then produces meaningless IntelliSense suggestions. After I renamed it back, the IS came back.