Added - Virtual Joystick for mobile device

Bugs or Develop. I am not sure which I should put it in.

1) input method

	The game used the Input Manager method, which is Input.GetAxis("Horizontal") & Input.GetAxis("Vertical") to control the player's movement. This method is the easiest to understand for newbies during my learning process. I respect that. However, once I had the game published online, I immediately thought I needed more than just the keyboard input method. I want to play the game on my phone.
	I searched the web for touchscreen input methods and found more YouTube Tutorials. Unity has a new input method - Input System that handles multi-input devices. This new method is more complicated than the one I used because you can create multi-maps and actions on different devices.

2) UI joystick

After knowing I could use the Unity Input System and a virtual UI joystick to simulate an input when on a mobile device, I started working on it immediately. 
Firstly, install the "input system" package. Bring up the Package Manager from the top menu bar - Window > Package Manager, select Packages: Unity Registry, and look for "Input System". Install the package to use it.
Then, add an input action to your asset. At the Assets window, left mouse click, Create > Input Actions.
A new window appears, and you can create the  Action Maps and Actions here.