Add extracted source directory and README navigation

extracted-source/node_modules/react-reconciler/cjs/react-reconciler-constants.production.js

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+/**
+ * @license React
+ * react-reconciler-constants.production.js
+ *
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+"use strict";
+exports.ConcurrentRoot = 1;
+exports.ContinuousEventPriority = 8;
+exports.DefaultEventPriority = 32;
+exports.DiscreteEventPriority = 2;
+exports.IdleEventPriority = 268435456;
+exports.LegacyRoot = 0;
+exports.NoEventPriority = 0;