chore: add README and images

Signed-off-by: Aditya Agarwal <[email protected]>

README.md

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+# Calibrate 3.5' LCD Touchscreen With Arduino UNO R3/R4
+
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+
+## Overview
+
+This repository contains a program to calibrate a 3.5' touch screen display shield, as shown below -
+
+|![Image of LCD Touch Shield from Top](images/LCD_top.png)|![Image of LCD Touch Shield from Bottom](images/LCD_bottom.png)|
+|-|-|
+
+Most 3.5' LCD Touch displays use the ILI9486 Display Driver and include a resistive touchscreen. **The PCB Layout & silkscreen text may vary slightly between displays. This does not change their behaviour and functionality.** This repository depends on the following libraries -
+
+- [Adafruit Touch Screen Library](https://github.com/adafruit/Adafruit_TouchScreen) to manage touch input
+- [Adafruit GFX Library](https://github.com/adafruit/Adafruit-GFX-Library/tree/master) for graphics primitives
+- [This fork of the MCUFriend KBV library](https://github.com/slviajero/MCUFRIEND_kbv) to drive the display (this makes it compatible with the UNO R4)
+
+The program has been written using PlatformIO, and has been tested on the [Arduino UNO R3](https://docs.arduino.cc/hardware/uno-rev3/), [Arduino UNO R4 Minima](https://docs.arduino.cc/hardware/uno-r4-minima/) & [Arduino UNO R4 WiFi](https://docs.arduino.cc/hardware/uno-r4-wifi/).
+
+## Building/Uploading With PlatformIO
+
+Since this project has been written using PlatformIO by default, simply run the following commands to fetch the libraries, build the project and upload the program -
+
+```shell
+pio pkg install
+pio run
+pio run --target upload
+```
+
+## Building/Uploading With Arduino IDE
+
+Create a new sketch and copy the contents of ```src/main.cpp``` from this repository into the default ```.ino``` file. Create a new tab/file in the IDE named ```constants.h``` and copy the contents of ```src/constants.h``` from this repository into this file.
+
+Install the Adafruit Touch Screen Library and Adafruit GFX Library from the Library Manager (under *Sketch>Include Library>Manage Libraries...*)
+
+Download [this](https://github.com/slviajero/MCUFRIEND_kbv) repository as a ZIP file and install it by navigating to *Sketch>Include Library>Add .ZIP Library*, and selecting the downloaded file from the file explorer.
+
+After this, you can Build and Upload the program as usual.
+
+
+## Using the Example
+
+As soon as the program is uploaded, the display should turn black and a red crosshair should appear at the top-left corner of the screen.
+
+Using the included plastic stylus, gently tap as close to the centre of the crosshair as possible. Life the stylus once the crosshair turns green. After this process is repeated 5 times, the crosshair should turn white.
+
+The program repeats this process for all 4 corners, and reports 4 values on the Serial Monitor as well as the display upon completion, namely ```XBEGIN```, ```XEND```, ```YBEGIN``` and ```YEND```. These values can be used along with the Adafruit Touch Screen Library to convert the coordinates from the touch screen library as follows -
+
+```cpp
+
+// this snippet uses the Adafruit Touch Screen Library
+// XP, YP, XM and YM are the pins used by the touchscreen
+// 300 is the resistance across the screen in ohms
+
+// create constants XBEGIN, XEND, YBEGIN and YEND according to the output from the calibration example
+
+TouchScreen ts = TouchScreen(XP, YP, XM, YM, 300);
+TSPoint p = ts.getPoint();
+
+touchX = p.x; // Raw Horizontal Coordinate
+touchY = p.y; // Raw Veritcal Coordinate
+
+touchX = constrain(p.x, XBEGIN, XEND);
+touchY = constrain(p.y, YBEGIN, YEND);
+
+touchX = map(touchX, XBEGIN, XEND, 0, 319); // Horizontal Coordinate of Touch
+touchX = map(touchX, XBEGIN, XEND, 479, 0); // Vertical Coordinate of Touch
+```
+
+## Troubleshooting
+
+Some common problems and their solutions -
+
+|Problem|Solution|
+|-|-|
+|Display stays white after uploading program|Non-Standard Driver (not ILI9486)|
+|Display not responding after touch|Try changing the order of the touch pins in ```src/constants.h``` file, i.e. swap the values of ```XP```, ```YP```, ```XM``` and ```YM```|
+|Compilation issues related to SPI|Update the Arduino IDE version and/or install the SPI library|
+|Display Flickering/Arduino is reset automatically|Faulty Power Supply/Cable|