[Project Update] Upload the Introduction of this project

Signed-off-by: Dragon1573 <Legend_1949@126.com>

Author: Dragon1573

README.md

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+# A Simple Plain-text Editor
+
+[![GitHub license](https://img.shields.io/github/license/Dragon1573/Text-Editor-JFX?label=License&style=flat-square)](https://github.com/Dragon1573/Text-Editor-JFX/blob/master/LICENSE)
+
+## Introduction
+
+This project is a reproduction of my Software Engineering Course Design, Semester 2. It provides an editor for users editing any kind of plain-text format files (not only `*.txt` but also `*.csv`, `*.md`, `*.rst`).
+
+I finished my first project (`v1.0`) with Swing and Java 8 Language Level, but I think the project is too complex for me to fix and upgrade. So I reproduce this project, recover all codes with JavaFX in Java 14 Language Level. 
+
+## User Instructions
+
+### Requirements
+
+- Java Runtime Environment 14 or above
+
+### Installation
+
+1. Install JRE 14 (any manufactures are acceptable, such as Oracle and OpenJDK) on your device.
+2. Download the latest release from [GitHub Releases](https://github.com/Dragon1573/Text-Editor-JFX/releases).
+3. Double-click the `*.jar` and launch the application.
+4. Enjoy your work!
+
+## Developer Guide
+
+### Requirements
+
+- Java Development Kit 14 (v14.0.1 is recommended) or above
+- Apache Maven 3 (v3.6.3 is recommended) or above
+- JetBrains IntelliJ IDEA (v2020.2 is recommended)
+
+You can use Eclipse IDE instead of JetBrains IDE, but I can't sure if it's compatible.
+
+### Installation
+
+- Clone this repository to your device.
+- Switch the working directory to where `pom.xml` is located in.
+- Launch a terminal and execute `mvn clean compile exec:exec` to launch the application.
+- Execute `mvn clean package` to create an executable, all-dependencies-included `*.jar` file.