Update comments for loaders webpack to clarify excluding file extensions

packages/react-scripts/config/webpack.config.dev.js

@@ -112,20 +112,14 @@ module.exports = {
       }
     ],
     loaders: [
-      // Default loader: load all assets that are not handled
-      // by other loaders with the url loader.
-      // Note: This list needs to be updated with every change of extensions
-      // the other loaders match.
-      // E.g., when adding a loader for a new supported file extension,
-      // we need to add the supported extension to this loader too.
-      // Add one new line in `exclude` for each loader.
-      //
-      // "file" loader makes sure those assets get served by WebpackDevServer.
-      // When you `import` an asset, you get its (virtual) filename.
-      // In production, they would get copied to the `build` folder.
-      // "url" loader works like "file" loader except that it embeds assets
-      // smaller than specified limit in bytes as data URLs to avoid requests.
-      // A missing `test` is equivalent to a match.
+      // ** ADDING/UPDATING LOADERS **
+      // The "url" loader handles all assets unless explicitly excluded.
+      // The `exclude` list *must* be updated with every change to loader extensions.
+      // When adding a new loader, you must add its `test` 
+      // as a new entry in the `exclude` list for "url" loader.
+
+      // "url" loader embeds assets smaller than specified size as data URLs to avoid requests.
+      // Otherwise, it acts like the "file" loader.
       {
         exclude: [
           /\.html$/,
@@ -179,6 +173,8 @@ module.exports = {
           name: 'static/media/[name].[hash:8].[ext]'
         }
       }
+      // ** STOP ** Are you adding a new loader?
+      // Remember to add the new extension(s) to the "url" loader exclusion list.
     ]
   },
   // @remove-on-eject-begin

packages/react-scripts/config/webpack.config.prod.js

@@ -120,18 +120,14 @@ module.exports = {
       }
     ],
     loaders: [
-      // Default loader: load all assets that are not handled
-      // by other loaders with the url loader.
-      // Note: This list needs to be updated with every change of extensions
-      // the other loaders match.
-      // E.g., when adding a loader for a new supported file extension,
-      // we need to add the supported extension to this loader too.
-      // Add one new line in `exclude` for each loader.
-      //
-      // "file" loader makes sure those assets end up in the `build` folder.
-      // When you `import` an asset, you get its filename.
-      // "url" loader works just like "file" loader but it also embeds
-      // assets smaller than specified size as data URLs to avoid requests.
+      // ** ADDING/UPDATING LOADERS **
+      // The "url" loader handles all assets unless explicitly excluded.
+      // The `exclude` list *must* be updated with every change to loader extensions.
+      // When adding a new loader, you must add its `test` 
+      // as a new entry in the `exclude` list in the "url" loader.
+
+      // "url" loader embeds assets smaller than specified size as data URLs to avoid requests.
+      // Otherwise, it acts like the "file" loader.
       {
         exclude: [
           /\.html$/,
@@ -189,6 +185,8 @@ module.exports = {
           name: 'static/media/[name].[hash:8].[ext]'
         }
       }
+      // ** STOP ** Are you adding a new loader?
+      // Remember to add the new extension(s) to the "url" loader exclusion list.
     ]
   },
   // @remove-on-eject-begin