Add toolkit in the index page and nav bar

Author: adpi2

_data/doc-nav-header.yml

@@ -37,6 +37,8 @@
       url: "/tutorials/scala-on-android.html"
     - title: Scala with Maven
       url: "/tutorials/scala-with-maven.html"
+    - title: Using the Scala Toolkit
+      url: "/toolkit/introduction.html"
 - title: Reference
   url: "#"
   submenu:

index.md

@@ -26,6 +26,10 @@ sections:
         description: "Learn Scala by reading a series of short lessons."
         icon: "fa fa-book-open"
         link: /scala3/book/introduction.html
+      - title: "Scala Toolkit"
+        description: "Sending HTTP requests, writing files, running processes, parsing JSON..."
+        icon: "fa fa-toolbox"
+        link: /toolkit/introduction.html
       - title: Online Courses
         description: "MOOCs to learn Scala, for beginners and experienced programmers."
         icon: "fa fa-cloud"