maven-assembly-plugin descriptor for a simple tarball with dependencies

Today I was trying to make a simple tarball of a project + its dependent jar using the maven-assembly-plugin. I know this is a terrible way to do anything, but hey, just in case someone else wants to do something just as terrible, here are my pom.xml and assembly.xml (the assembly descriptor):

$ tree
.
├── assembly.xml
├── pom.xml
└── src
    └── main
        └── java
            └── AssemblyExample.java

$ cat pom.xml
<project
    xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd"
>
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.example</groupId>
    <artifactId>myproject</artifactId>
    <name>My Projects</name>
    <version>0.1</version>
    <build><plugins><plugin>
        <artifactId>maven-assembly-plugin</artifactId>
        <version>2.2.1</version>
        <configuration><descriptors>
            <descriptor>assembly.xml</descriptor>
        </descriptors></configuration>
        <executions> <execution>
            <phase>package</phase>
            <goals><goal>attached</goal></goals>
        </execution></executions>
    </plugin></plugins></build>
    <dependencies>
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-log4j12</artifactId>
            <version>1.7.2</version>
        </dependency>
    </dependencies>
</project>

$ cat assembly.xml
<?xml version="1.0" encoding="UTF-8"?>
<assembly>
    <id>ap3</id>

    <formats>
        <format>tar.gz</format>
    </formats>

    <includeBaseDirectory>true</includeBaseDirectory>

    <dependencySets>
        <dependencySet>
            <outputDirectory>jars</outputDirectory>
            <scope>runtime</scope>
        </dependencySet>
    </dependencySets>

</assembly>

$ mvn package
...
[INFO] Compiling 1 source file to /home/andrebal/Desktop/assemblyexample/target/classes
[INFO] 
...
[INFO] Building jar: /home/andrebal/Desktop/assemblyexample/target/myproject-0.1.jar
...
[INFO] --- maven-assembly-plugin:2.2.1:attached (default) @ myproject ---
[INFO] Reading assembly descriptor: assembly.xml
[INFO] Building tar : /home/andrebal/Desktop/assemblyexample/target/myproject-0.1-ap3.tar.gz
...
[INFO] BUILD SUCCESS

$ tar -tzf target/myproject-0.1-ap3.tar.gz 
myproject-0.1/jars/slf4j-log4j12-1.7.2.jar
myproject-0.1/jars/slf4j-api-1.7.2.jar
myproject-0.1/jars/log4j-1.2.17.jar
myproject-0.1/jars/myproject-0.1.jar