DC Motor 120rpm FIT0450 Add program to calculate angular speed and angle

Hello, DFRobot team.

I'm suggesting an improvement to your DC motor documentation wiki https://wiki.dfrobot.com/Micro_DC_Motor_with_Encoder-SJ01_SKU__FIT0450

I would like to add my program that I created while was doing my ROS2 robot running LattePanda Delta 3 board. This robot is using two FIT0450 DC motors with encoders. This demo program uses already existing program from the docs page, but I added additional functions to calculate angular speed and angle. I think it will bring to the DIY robotics developers more capabilities to build robots and improve quality of your product. Here is a Github link with Arduino program, feel free to comment and share your thoughts.

https://github.com/maxxlife/dfrobot_encoder_motor