update javadocs for xmlunit-assertj3

pom.xml

@@ -260,7 +260,11 @@
                 <packages>org.xmlunit.matchers*</packages>
               </group>
               <group>
-                <title>XMLUnit AssertJ Assertions ${project.version}</title>
+                <title>XMLUnit AssertJ 3.x Assertions ${project.version}</title>
+                <packages>org.xmlunit.assertj3*</packages>
+              </group>
+              <group>
+                <title>XMLUnit AssertJ 2.x/3.x Assertions ${project.version}</title>
                 <packages>org.xmlunit.assertj*</packages>
               </group>
               <group>

src/main/javadoc/overview.html

@@ -3,7 +3,7 @@
     <a href="https://www.xmlunit.org/">XMLUnit</a> helps testing code
     that creates XML.
 
-    <p>XMLUnit for Java is separated into three jars:</p>
+    <p>XMLUnit for Java is separated into several jars:</p>
     <ul>
       <li><code>xmlunit-core</code> contains all algorithms and
         classes needed to validate XML, perform XPath queries or
@@ -15,7 +15,12 @@
         supposed to work with Hamcrest 2.x as well.</li>
       <li><code>xmlunit-assertj</code>
         contains <a href="https://joel-costigliola.github.io/assertj/index.html">AssertJ</a>
-        assertions on top of <code>xmlunit-core</code>.</li>
+        assertions on top of <code>xmlunit-core</code> that work with
+        AssertJ 2.x and 3.x.</li>
+      <li><code>xmlunit-assertj3</code>
+        contains <a href="https://assertj.github.io/doc/">AssertJ
+        3.x</a> assertions on top of <code>xmlunit-core</code> that
+        work with AssertJ 3.18.1 and later.</li>
     </ul>
 
     <p>While XMLUnit is focussed on testing, parts of it may be useful