Documentation: Review contents and English expression for doc/2_vehicle_model

[ShisatoYano]

I am looking for a contributor to review the following documentation about source code implementation of vehicle model.
https://github.com/ShisatoYano/AutonomousVehicleControlBeginnersGuide/tree/main/doc/2_vehicle_model

Please review the following items:

• The existing contents are written correctly following the current source code: https://github.com/ShisatoYano/AutonomousVehicleControlBeginnersGuide/tree/main/src/components/vehicle
• Overall English grammars and words

If you find any mistakes or parts that could be phrased better, please create a pull request to update with the documentation label.