Merged in JChoclin/gazebo_tutorials/dev_files_for_topics_subscribe (pull request #477)

Suggest download dev files in topic subscribe

Approved-by: Louise Poubel <[email protected]>
Approved-by: Ian Chen <[email protected]>

Author: iche033

topics_subscribe/tutorial.md

@@ -16,6 +16,12 @@ gz topic -l
 
 This example subscribes to a [WorldStatistics message](http://gazebosim.org/api/msgs/dev/world__stats_8proto.html) and assumes that you can link against Gazebo.
 
+First, if you installed Gazebo from debians, make sure you've installed the Gazebo development files. If you installed Gazebo from source, you can ignore this step. Replace X with whatever version number of Gazebo you have.
+
+~~~
+sudo apt-get install libgazeboX-dev
+~~~
+
 Download `listener.cc` and `CMakeLists.txt` and put them into to a folder
 called `listener` at your home directory and then compile the example: