Add C++ to Rust cheat sheet to footer

Author: mre

templates/base.html

@@ -204,6 +204,7 @@ <h3>Migration Guides</h3>
                     <li><a href="/learn/migration-guides/typescript-to-rust/">TypeScript</a></li>
                     <li><a href="/learn/migration-guides/java-to-rust/">Java</a></li>
                     <li><a href="/learn/migration-guides/scala-to-rust/">Scala</a></li>
+                    <li><a href="/learn/migration-guides/cpp-to-rust/">C++</a></a></li>
                 </ul>
             </div>