Add toolkit in the index page and nav bar

Author: adpi2

_data/doc-nav-header.yml

@@ -31,6 +31,8 @@
       url: "/getting-started/intellij-track/getting-started-with-scala-in-intellij.html"
     - title: Getting Started with Scala and sbt
       url: "/getting-started/sbt-track/getting-started-with-scala-and-sbt-on-the-command-line.html"
+    - title: Using the Scala Toolkit
+      url: "/toolkit/introduction.html"
     - title: Scala for Java Programmers
       url: "/tutorials/scala-for-java-programmers.html"
     - title: Scala on Android

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"