Add extracted source directory and README navigation

extracted-source/node_modules/lodash-es/_flatRest.js

@@ -0,0 +1,16 @@
+import flatten from './flatten.js';
+import overRest from './_overRest.js';
+import setToString from './_setToString.js';
+
+/**
+ * A specialized version of `baseRest` which flattens the rest array.
+ *
+ * @private
+ * @param {Function} func The function to apply a rest parameter to.
+ * @returns {Function} Returns the new function.
+ */
+function flatRest(func) {
+  return setToString(overRest(func, undefined, flatten), func + '');
+}
+
+export default flatRest;