Add maven release plugin.
diff --git a/pom.xml b/pom.xml
index acea47d..7f4d3f5 100644
--- a/pom.xml
+++ b/pom.xml
@@ -6,9 +6,6 @@
   <groupId>net.hydromatic</groupId>
   <artifactId>optiq</artifactId>
   <packaging>jar</packaging>
-
-  <!-- Version number. The version number committed to github should be
-       TRUNK-SNAPSHOT except, briefly, when making a release. Next: 0.4.7. -->
   <version>TRUNK-SNAPSHOT</version>
 
   <!-- More project information. -->
@@ -269,6 +266,11 @@
           </execution>
         </executions>
       </plugin>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-release-plugin</artifactId>
+        <version>2.4.1</version>
+      </plugin>
     </plugins>
 
     <resources>