Update README.md to add Codementor

Codementor is an educational platform where junior developers can find senior developers to improve coding skills and get help with ongoing projects. Its main mission is to help aspiring developers grow faster by getting guidance from seasoned developers.

Author: christineshu

README.md

@@ -209,6 +209,9 @@
       <li>
         <a href="https://hackr.io/" target="blank">Hackr.io</a> - We at Hackr.io aggregate courses from many providers to make it easy to find the best courses on almost any subject, wherever they exist on the web.
       </li>
+      <li>
+        <a href="https://www.codementor.io/experts" target="blank">Codementor</a> - Get 1-on-1 expert help from senior developers to improve your coding skills or get help with your ongoing projects.
+      </li>
     </ol>
   </details>
   <details open>