To generate the Business Process Model report as part of the site generation, add the following in the <reporting> section of your POM:
<project>
[...]
<reporting>
<plugins>
<plugin>
<groupId>com.github.jonasrutishauser.maven.plugin</groupId>
<artifactId>bpmn-maven-plugin</artifactId>
<version>2.0.0</version>
</plugin>
</plugins>
</reporting>
[...]
</project>
When mvn site is invoked, the report will automatically be included in the Project Reports menu.
The plugin can also generate the report using its standalone goal:
mvn com.github.jonasrutishauser.maven.plugin:bpmn-maven-plugin:report
A HTML report should be generated in ${basedir}/target/site/business-process-models.html.