Update java.md

Added step to run the program correctly

content/influxdb/cloud-serverless/reference/client-libraries/v3/java.md

@@ -91,3 +91,11 @@ public class HelloInfluxDB {
   }
 }
 ```
+## Running the program
+
+Build the project and then run the executable .jar file with this [JVM Flag](https://arrow.apache.org/docs/java/install.html). 
+<br/><br/> 
+**Example:**
+```sh
+  java --add-opens=java.base/java.nio=org.apache.arrow.memory.core,ALL-UNNAMED -jar target/{your-jar-file}.jar
+```