Clarify "Getting Started" launch file change (#37)

* Clarify "Getting Started" launch file change

The added note should help new users or ROS 2 Dashing users avoid issues with
the "Getting Started" launch file, and also explain preference for Eloquent
and later.

ros-navigation/navigation2#1607
ros-navigation/navigation2#1663
#9
#36

* Avoid recommending a specific ROS 2 distro

Updated based on comments from the pull request.

#37

getting_started/index.rst

@@ -51,6 +51,14 @@ Running the Example
    .. code-block:: bash
 
       ros2 launch nav2_bringup tb3_simulation_launch.py
+   
+   .. note::
+
+      For ``ROS 2 Dashing Diademata`` or earlier, use
+      ``nav2_simulation_launch.py``.
+      However, it is recommended to use the most recent `ROS 2 LTS distribution
+      <https://ros.org/reps/rep-2000.html>`_  for improved stablity and feature
+      completeness.
 
    This launch file will launch Navigation2 with the AMCL localizer in the
    ``turtlebot3_world`` world.