Add extracted source directory and README navigation

extracted-source/node_modules/highlight.js/lib/languages/plaintext.js

@@ -0,0 +1,19 @@
+/*
+Language: Plain text
+Author: Egor Rogov (e.rogov@postgrespro.ru)
+Description: Plain text without any highlighting.
+Category: common
+*/
+
+function plaintext(hljs) {
+  return {
+    name: 'Plain text',
+    aliases: [
+      'text',
+      'txt'
+    ],
+    disableAutodetect: true
+  };
+}
+
+module.exports = plaintext;