docs: include available objects in documentation

docs/plugins/raw-loader.js

@@ -0,0 +1,12 @@
+module.exports = function (context, options) {
+  return {
+    name: 'labelmap',
+    configureWebpack(config, isServer, utils) {
+      return {
+        module: {
+          rules: [{ test: /\.txt$/, use: 'raw-loader' }],
+        },
+      };
+    },
+  };
+};