Added useful links to landing page (#559)

* added useful links to landing page

* GitHub should have a capital h

* Updated ember core docs link to 'release' version

* Simplify "Useful Links"

Author: honeyspoon

app/templates/project-version/index.hbs

@@ -36,4 +36,17 @@
   <p>
     The most up-to-date and complete mappings between the previous API and the new JavaScript Modules API can be found at the <a href='https://github.com/ember-cli/ember-rfc176-data'>ember-rfc176-data</a> repository.  <a href='https://github.com/tomdale/ember-modules-codemod'>Codemod tooling</a> is also available to help migrate existing Ember projects to the new JavaScript Modules API syntax.
   </p>
+  <h2>Useful links</h2>
+  <ul>
+    <li>
+      <h5>
+        <a href="https://github.com/ember-learn/ember-api-docs">API Documentation Github Repository</a>
+      </h5>
+    </li>
+    <li>
+      <h5>
+        <a href="https://guides.emberjs.com/release/getting-started/core-concepts/">Ember Core Concepts</a>
+      </h5>
+    </li>
+  </ul>
 </article>