Update README

README.md

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 # fxKeyboard
+
 Use fx-9860 series calculator as a keybord for computer.
+
+**WARNING: THIS TOOL MAY DAMAGE YOUR CALCULATOR OR COMPUTER. ALWAYS FOLLOW THE DOC AND I WILL NOT BE RESPONSIBLE FOR ANY DAMAGE.**
+
+## Usage
+
++ Use FA-124 software to copy the Add-in to your calculator.
++ Use the LINK app in calcutor menu to connect the calculator to your computer.
++ *READ NOTICE BEFORE THIS STEP!* Download Zadig from [here](https://zadig.akeo.ie/). Open Zadig, click Options - List All Device, select CESG502, and replace the original driver with WinUSB.
++ Open the Add-in in your calculator. It will automatically connect to your computer. If you didn't plug the USB cable, it will exit after a short time.
++ Open the fxKeyboardLink software in your computer. Now you can use your calculator as a keybord for your computer.
++ Some special keyboard mapping:
+
+  | Calculator Key | Computer |
+  | ---- | ---- |
+  | OPTN | Switch between arrow mode and cursor mode |
+  | Arrow keys | Arrow keys in arrow mode and cursor controller in cursor mode |
+  | θ | Text: theta |
+  | EXIT | ESC |
+  | QUIT | ESC |
+  | ∠ | < |
+  | sin-1 | Text: arcsin |
+  | ab/c | / |
+  | CAPTURE | PrintScreen |
+  | CLIP | Ctrl + C |
+  | PASTE | Ctrl + V |
+  | DEL | Backspace |
+  | INS | Insert |
+  | ÷ | / |
+  | π | pi |
+  | EXE | Enter in arrow mode and click in cursor mode
+  | EXE with SHIFT | Enter with Shift pressed. This is convenient for using Mathmetica
+
+
+## Notice
+
++ This tool will automatically open the NumLock in your computer.
++ Once your use Zadig to replace the original driver, you can't use FA-124 to link your calculater. If you want to get back to the original driver, follow Zadig's FAQ [here](https://github.com/pbatard/libwdi/wiki/FAQ#Help_Zadig_replaced_the_driver_for_the_wrong_device_How_do_I_restore_it) carefully. You need to know that the USB device is CESG502.
++ If you can't connect your calculator to your computer in any way, try to restart your calculator by the button behind.
+
+## Known Issue
+
++ Press the calculator key down continously will not work like that in your computer. The reason is that I only used GetKey function in this Add-in.
++ In cursor mode, the cursor moved slowly in a constant speed.
++ I would be glad if someone can fix the issues above.
+
+## Thanks
+
+Thanks Simon Lothar for his great work in syscall.
+
+## Build
+| Software | Tool |
+| ---- | ---- |
+| Add-in: fxKeyboardAddin | fx-9860G Software Development Kit |
+| Win32: fxKeyboardLink | Visual Studio 2019 with libusb-1.0 |