(doc) Fixes in multirelease page

[pzygielo]

• Run mvn clean verify to make sure basic checks pass. A more thorough check will be performed on your pull request automatically.
  (Previous faillure due to missing env var JAVA_HOME expected in

  maven-compiler-plugin/src/test/java/org/apache/maven/plugin/compiler/CompilerMojoTestCase.java

  Line 213 in 1455594

  setVariableValueToObject( compileMojo, "executable", new File( System.getenv( "JAVA_HOME" ), "bin/javac" ).getPath() );

  )
  I also ran mvn site -DskipTests=true to observe my changes in produced target/site/multirelease.html.

• You have run the integration tests successfully (mvn -Prun-its clean verify).

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[pzygielo]

Changes without line splitting commits: master...41e3afb