docs: add project documentation

docs/INSTALLATION.md

@@ -0,0 +1,42 @@
+# Installation
+
+## Requirements
+
+- Docker Engine
+- Docker Compose
+- Java 21 and Node.js/npm if building the application locally
+
+## Build the application
+
+From the repository root:
+
+```bash
+cd backend
+./gradlew clean build
+cd ..
+```
+
+The Gradle build also builds the Angular frontend and packages its production assets into the Spring Boot application.
+
+## Start with Docker Compose
+
+```bash
+docker compose up -d --build
+```
+
+The default Compose configuration maps host port `8088` to container port `8080`.
+
+Open http://localhost:8088 in your browser.
+
+## Check status and logs
+
+```bash
+docker compose ps
+docker compose logs -f htop-web
+```
+
+## Stop the application
+
+```bash
+docker compose down
+```