[#6690] add versionadded directive

Author: xabbuh

components/console/introduction.rst

@@ -232,6 +232,10 @@ level. For example::
     // alternatively you can pass the verbosity level to writeln()
     $output->writeln('...', OutputInterface::VERBOSITY_VERBOSE);
 
+.. versionadded:: 2.8
+    The ability to pass the verbosity level to the ``writeln()` method was
+    introduced in Symfony 2.8.
+
 There are also more semantic methods you can use to test for each of the
 verbosity levels::