On WebEditor
On the left : Librairies
I choose library and I Download my library. (I don't know where to download it, but I've put it in .zip in a "libraries" folder I've created)
Then i click on Include, this line is added : #include <Arduino_FreeRTOS.h>
But it doesn't want to compile.
it depends on what platform are you working on, assuming you are working with Arduino IDE, the libraries folder is located at the same place where your sketches are.