Adding a static js script to a custom visualization

Hi,

I have followed the instructions on this page: https://github.com/Microsoft/PowerBI-visuals/blob/master/Tutorial/ExternalLibraries.md, i.e.:

* Created a folder external in the viz. folder (same level as e.g. src and style).

* Copied my wanted library to this new folder (./external/d3.v4.min.js).

* Added the corresponding line to tsconfig.json, resulting in

{
  "compilerOptions": {
    "allowJs": true,
    "emitDecoratorMetadata": true,
    "experimentalDecorators": true,
    "target": "ES5",
    "sourceMap": true,
    "out": "./.tmp/build/visual.js"
  },
  "files": [
    ".api/v1.3.0/PowerBI-visuals.d.ts",
    "src/visual.ts",
    "external/d3.v4.min.js"
  ]
}

However, I still get the compilation error "Cannot find name `d3`".

I don't want to use npm or typings (and as I understand from  https://github.com/Microsoft/PowerBI-visuals/blob/master/Tutorial/ExternalLibraries.md that should not be necessary for loading external libraries).

What am I missing? Do I have to load it explicitly in src/visual.ts in some way?

Thanks!