Detail README.md

Author: JRomainG

README.md

@@ -1,2 +1,35 @@
 # Watermarker
-Lightweight PDF & image watermarker for macOS
+
+Lightweight PDF & image watermarker for macOS, built using [SwiftUI](https://developer.apple.com/xcode/swiftui)
+
+## Preview
+
+<table style="border: none">
+  <tr style="border: none">
+    <td style="border: none"><img src="img/preview-1.png"></td>
+    <td style="border: none"><img src="img/preview-2.png"></td>
+  </tr>
+</table>
+
+## Installing
+
+Simply grab the latest version from the [release page](https://github.com/JRomainG/Watermarker/releases) (or click [here](https://github.com/JRomainG/Watermarker/releases/latest/download/Watermarker.app.zip)).
+
+## Development
+
+To install, simply checkout the `dev` branch of this repository:
+
+```bash
+git clone https://github.com/JRomainG/Watermarker.git
+git checkout dev
+```
+
+You will then be able to open the `Watermarker.xcodeproj` project. Swift's package manager should automatically download [swift-collections.git](https://github.com/apple/swift-collections.git). Don't forget to change the team and signing certificate before building.
+
+## Contributing
+
+If you found a bug, or would like to see a new feature added, feel free to open an issue on the Github page. Pull requests are welcome!
+
+## License
+
+The project is available under the [GPLv3](https://www.gnu.org/licenses/gpl-3.0.en.html) license.