Document how to install the simulator libraries (if people want to)

Author: PeterJCLaw

simulator/setting_up_simulator.md

@@ -26,6 +26,8 @@ You will also need Python installed.
 There are a small number of [external libraries]({{ site.baseurl }}/kit/brain_board/python_libraries) which will be available to your robot code during the competition.
 Note that for local development you will need to install these yourself.
 
+Once you have downloaded the simulation, the libraries can be installed with `pip install -r competition-simulator.../libraries.txt`.
+
 ## Installing the simulation
 
 1. Create a directory, perhaps called `simulation` where you will store your robot code.
@@ -35,6 +37,7 @@ Note that for local development you will need to install these yourself.
     simulation
     ├── competition-simulator-<version>
     │   ├── ...
+    │   └─ libraries.txt
     │   └─ worlds
     │       └── Arena.wbt
     └── robot.py