docs: expand README with build instructions, tech stack, and test info

README.md

@@ -1,5 +1,47 @@
-### JavaFX Calculator 
+# JavaFX Calculator
 
-The implementation of a given JavaFX project. It simulates a calculator with four binary operations, i.e. addition, subtraction, multiplication and division, and two unary operations, i.e. the square root and negation of an input number.
+A calculator built with JavaFX 17 and Maven (University of Kent, CO871 Assignment 2). Implements four binary operations and two unary operations with a clean FXML-driven UI.
 
-![Image of Calculator](/Calculator.png)
+![Screenshot of calculator UI](Calculator.png)
+
+## Operations
+
+| Type | Operations |
+|------|-----------|
+| Binary | Addition, subtraction, multiplication, division |
+| Unary | Square root, negation |
+
+## Requirements
+
+- Java 17
+- Maven 3.6 or later (or use the included Maven Wrapper)
+
+## Build and run
+
+```bash
+mvn clean javafx:run
+```
+
+Using the Maven Wrapper:
+
+```bash
+./mvnw clean javafx:run    # macOS / Linux
+mvnw.cmd clean javafx:run  # Windows
+```
+
+## Tests
+
+JUnit Jupiter 5 tests exercise all operations and edge cases:
+
+```bash
+mvn test
+```
+
+## Tech stack
+
+| Component | Version |
+|-----------|---------|
+| Java | 17 |
+| JavaFX (controls + FXML) | 17.0.2 |
+| JUnit Jupiter | 5.8.2 |
+| Build tool | Maven |