Apply suggestions from code review

Co-authored-by: Oskar Stark <oskarstark@googlemail.com>

Author: loic425

serializer.rst

@@ -499,9 +499,9 @@ given class:
 
 .. code-block:: terminal
 
-    $ php bin/console debug:serializer 'App\Entity\SomeClass'
+    $ php bin/console debug:serializer 'App\Entity\Book'
 
-        App\Entity\SomeClass
+        App\Entity\Book
         --------------------
 
         +----------------+------------------------------------------------------------+
@@ -532,7 +532,7 @@ given class:
 
 .. versionadded:: 6.3
 
-    This debug command was introduced in Symfony 6.3.
+    The debug:serializer`` command was introduced in Symfony 6.3.
 
 
 Going Further with the Serializer