Add documentation for the new maven integration goals take 2

This is a replacement for #160 without integration tests for the examples. I unzipped the produced `org.jacoco.examples-0.6.4-SNAPSHOT.zip` and ran `mvn -f pom.xml clean verify` which only produced coverage for the unit tests and `mvn -f pom-it.xml clean verify` which produced the two coverage reports for unit and integration tests.