Update configuration.md to include an example of generating sourcemaps with Embroider

I had to add devtool to my webpackConfig in order for  sourcemaps to be generated of my typescript files with Embroider. 

Not sure if this documentation belongs here or in the embroider docs (or whether there are other/better ways to set up the config)

Author: johanrd

tests/dummy/app/templates/docs/configuration.md

@@ -54,5 +54,17 @@ const app = new EmberApp(defaults, {
 
 (Note that this _will_ noticeably slow down your app rebuilds.)
 
+If you are using [Embroider](https://github.com/embroider-build/embroider), you might need to inlcude [devtool](https://webpack.js.org/configuration/devtool/) in your webpack configuration:
+
+```ts
+return require('@embroider/compat').compatBuild(app, Webpack, {
+  packagerOptions: {
+    webpackConfig: { 
+      devtool: 'source-map'
+    }
+  }
+}
+```
+
 If you're updating from an older version of the addon, you may also need to update your `tsconfig.json`. (Current versions generate the correct config at installation.) Either run `ember generate ember-cli-typescript` or verify you have the same sourcemap settings in your `tscsonfig.json` that appear in [the blueprint](https://github.com/typed-ember/ember-cli-typescript/blob/master/blueprints/ember-cli-typescript/files/tsconfig.json).