Fox example in quickStart for Scala 3

- Fix the example on the quickStart page
- Mention version of Scala in the examples on the index and the
  quickStart pages

Author: giner

app/views/index.scala.html

@@ -69,7 +69,7 @@
 To maximize your productivity, ScalaTest uses its own extension points to support several styles of testing out of the box.
 You can select whatever style best fits your team's experience and culture. For instance, the above example
 uses <code>FlatSpec</code>, a good choice for teams wishing to move from XUnit to BDD.  When
-you run it, you get an informal specification of the software being tested:
+you run it, you get an informal specification of the software being tested (the example assumes you are using Scala @{majorMinorScalaVersion}):
 </p>
 </div>
 

app/views/quickStart.scala.html

@@ -71,12 +71,12 @@ <h1>ScalaTest quick start</h1>
 <p>
 To run it, you will need one more artifact,
 <a href="@{quickStartXmlJar}">the Jar file for Scala's XML module</a>.
-Once you've downloaded that Jar file, you can run <code>ExampleSpec</code> like this:
+Once you've downloaded that Jar file, you can run <code>ExampleSpec</code> like this (the example assumes you are using Scala @{majorMinorScalaVersion}):
 </p>
 
 <pre class="scala">
 $ CLASSPATH=scalatest-app_@{majorMinorScalaVersion}-@{latestVersion}.jar:scala-xml_3-2.3.0.jar
-$ scala -cp $CLASSPATH org.scalatest.run ExampleSpec
+$ scala -cp $CLASSPATH --main-class org.scalatest.run -- ExampleSpec
 <span class="cyanincolor">Run starting. Expected test count is: 2</span>
 <span class="greenincolor">ExampleSpec:
 A Stack