Add example of exports.types field (#992)

* Add example of exports.types field

* Update README.md

Co-authored-by: Ryan Christian <33403762+rschristian@users.noreply.github.com>

Author: jeffposnick

README.md

@@ -166,12 +166,13 @@ The filenames and paths for generated bundles in each format are defined by the
   "source": "src/index.js",             // input
   "main": "dist/foo.js",                // CommonJS output bundle
   "umd:main": "dist/foo.umd.js",        // UMD output bundle
-  "module": "dist/foo.mjs",           // ES Modules output bundle
+  "module": "dist/foo.mjs",             // ES Modules output bundle
   "exports": {
+    "types": "./dist/foo.d.ts",         // TypeScript typings for NodeNext modules
     "require": "./dist/foo.js",         // CommonJS output bundle
     "default": "./dist/foo.modern.mjs", // Modern ES Modules output bundle
   },
-  "types": "dist/foo.d.ts"              // TypeScript typings directory
+  "types": "dist/foo.d.ts"              // TypeScript typings
 }
 ```
 
@@ -230,6 +231,8 @@ To ensure Microbundle does not process extraneous files, by default it only incl
 
 If you're using TypeScript with CSS Modules, you will want to set `"include": ["node_modules/microbundle/index.d.ts"]` in your `tsconfig.json` to tell TypeScript how to handle your CSS Module imports.
 
+To ensure that your module's `.d.ts` type info is visible to other TypeScript projects that use [`moduleResolution: 'NodeNext'`](https://www.typescriptlang.org/docs/handbook/esm-node.html), add a [`types` key](https://www.typescriptlang.org/docs/handbook/esm-node.html#packagejson-exports-imports-and-self-referencing) to your `package.json`'s corresponding `exports` mapping.
+
 ### CSS and CSS Modules
 
 Importing CSS files is supported via `import "./foo.css"`. By default, generated CSS output is written to disk. The `--css inline` command line option will inline generated CSS into your bundles as a string, returning the CSS string from the import: