pypot seems required even in fake mode, yet it's not installed by default

[RemiFabre]

Unless this is a weird side effect on the headless computer, after following the installation process and running:

ros2 launch reachy_bringup reachy.launch.py  fake:=true start_rviz:=false

I get:

[INFO] [launch]: All log files can be found below /home/bedrock/.ros/log/2023-08-23-16-01-28-995604-bedrock-31749
[INFO] [launch]: Default logging verbosity is set to INFO
Waiting for reachy_discovery to finish...
Process Process-1:
Traceback (most recent call last):
  File "/usr/lib/python3.10/multiprocessing/process.py", line 314, in _bootstrap
    self.run()
  File "/usr/lib/python3.10/multiprocessing/process.py", line 108, in run
    self._target(*self._args, **self._kwargs)
  File "/home/bedrock/reachy_ws/install/reachy_bringup/share/reachy_bringup/launch/reachy.launch.py", line 35, in run_get_missing_motors_reachy
    from reachy_utils.discovery import get_missing_motors_reachy
  File "/home/bedrock/reachy_ws/build/reachy_utils/reachy_utils/discovery.py", line 7, in <module>
    from pypot.dynamixel import DxlIO, Dxl32

Also I had to create a .reachy.yaml file for this same fake:=true command to work.

If theses dependencies are needed, we should add them to the installation guide