Add tutorial on how to a migrate ROS 2 package that uses Gazebo Classic

Signed-off-by: Addisu Z. Taddese <addisu@openrobotics.org>

Author: azeey

harmonic/index.yaml

@@ -94,3 +94,7 @@ pages:
       - name: ros_gz_project_template_guide
         title: ROS 2 integration template
         file: ros_gz_project_template_guide.md
+      - name: ros2_migration_from_gazebo_classic
+        title: Migrating ROS 2 packages that use Gazebo Classic
+        file: ros2_migration_from_gazebo_classic.md
+        description: Migrating ROS 2 packages that use Gazebo Classic (gazebo_ros_pkgs) to Gazebo (ros_gz)

index.yaml

@@ -23,6 +23,10 @@ pages:
     title: ROS/Gazebo Installation
     file: ros_installation.md
     description: Our development plans.
+  - name: migrating_gazebo_classic_ros2_packages
+    title: Migration from ROS 2 Gazebo Classic
+    file: migrating_gazebo_classic_ros2_packages.md
+    description: A tutorial on how to migrate a ROS 2 package that uses Gazebo Classic to the new Gazebo
   - name: roadmap
     title: Roadmap
     file: roadmap.md