Mentioned Vulkan drawbacks and solutions

Author: fdomf

_posts/2019-07-10-release-0.9.6.md

@@ -390,11 +390,13 @@ Check it out in our [documentation](https://carla.readthedocs.io/en/latest/pytho
 It is possible to run CARLA with Vulkan **(experimental)** or OpenGL. Vulkan performs faster than OpenGL but, as it is an experimental build,
 there may be some graphical or memory consuming bugs that may affect the user experience when working with CARLA.
 
+Vulkan will prevent CARLA to run off-screen and in Docker, so to run them it is needed to use OpenGL. Therefore the `-opengl` flag must be activated.
+
 **Disclaimer:** Despite being an experimental build, Vulkan is the preferred API to run CARLA simulator.
 
 Don't forget that there are two graphic quality levels, `Epic` and `Low`.
 
-Check it out in our [documentation](https://carla.readthedocs.io/en/latest/configuring_the_simulation/#graphics-quality)!
+More information about Vulkan and OpenGL in our [documentation](https://carla.readthedocs.io/en/latest/configuring_the_simulation/#graphics-quality)!
 
 ### Full list of changes