Update README.md

As suggested by @tallesh in #135

README.md

@@ -53,9 +53,11 @@ For more information on the security details visit [cryptomator.org](https://cry
 
 ```
 cd main
-mvn clean install
+mvn clean install -Prelease
 ```
 
+An executable jar file will be created inside `main/uber-jar/target`.
+
 ## Contributing to Cryptomator
 
 Please read our [contribution guide](https://github.com/cryptomator/cryptomator/blob/master/CONTRIBUTING.md), if you would like to report a bug, ask a question or help us with coding.