Setup instructions: PX4 SITL

If you intend to use software in the loop with PX4 (for example, to simulate in Gazebo), you also need the PX4 repository. Follow the instruction to install it:

$ sudo apt install libgstreamer1.0-dev
$ cd ~/catkin_ws/src
$ git clone https://github.com/PX4/Firmware.git
$ cd Firmware
$ git checkout v1.10.2
$ git submodule update --init --recursive
$ make
$ make px4_sitl_default gazebo
$ cd ~/catkin_ws
$ catkin_make

You should be seeing a SITL simulation in Gazebo, but this is not what we want as it's not within ROS, so kill it and then...