README update

README.md

@@ -1,11 +1,41 @@
 # librewatmark
 
-Tool to put a watermark on sensitive documents. Useful to mitigate identity theft etc.
+Tool to put a watermark on sensitive documents. Useful to avoid identity theft. 
 
 Some services for this already exist on the Web, but then you have to trust them. Here the program runs on your machine, offline.
 
-Using the ImageJ library.
+Example result:
+
+(some image)
+
+## Compilation
+
+Install Java and Maven on your system. Then, in the root directory, generate a JAR file:
+
+```
+mvn clean package
+```
+
+You can then execute it using:
+
+```
+java -jar target/librewatermark-1.0-SNAPSHOT.jar
+```
+
+To create an executable for your platform, do:
+
+```
+jpackage --name librewatmark --input target --main-jar librewatermark-1.0-SNAPSHOT.jar --main-class org.whatever.Main --type TYPE
+```
+
+Where `TYPE` can be `deb` for Debian-based GNU/Linux distributions, `app-image` for the AppImage format, `rpm` for Fedora and friends, `dmg` for MacOS, and `exe` for Windows.
 
 ## Usage
 
-Install Java on your system. Then run the jar file provided in Releases.
+The program takes an input image, a watermark string using the `-s` option, and optionally an output filename with the `-o` option. When no output filename is specified, the default is the input filename + "-watermark".
+
+```
+$ librewatmark
+librewatmark - libre watermark tool
+Usage: <input file> -s <string> [-o <output file>]
+```