Add links to the new API docs (#257)

Author: aabounegm

hugo/content/api/_index.md

@@ -0,0 +1,5 @@
+---
+title: "API"
+weight: 300
+---
+<meta http-equiv="refresh" content="0; url=https://eclipse-langium.github.io/langium/"/>

hugo/layouts/partials/langium-mobile-menu.html

@@ -36,6 +36,9 @@
                 <a href="/playground/" class="nav-link-mobile">
                     Playground
                 </a>
+                <a href="https://eclipse-langium.github.io/langium/" class="nav-link-mobile">
+                    API
+                </a>
                 <a href="https://www.typefox.io/language-engineering/" class="nav-link-mobile">
                     Support
                 </a>

hugo/layouts/partials/langium-nav.html

@@ -8,6 +8,9 @@
     <a href="/playground/" class="nav-link-desktop">
         Playground
     </a>
+    <a href="https://eclipse-langium.github.io/langium/" class="nav-link-desktop">
+        API
+    </a>
     <a href="https://www.typefox.io/language-engineering/"
         class="nav-link-desktop text-emeraldLangium dark:text-emeraldLangium">
         Support