minor #23833 [DI] Fix some docblocks (nicolas-grekas)

This PR was merged into the 3.3 branch.

Discussion
----------

[DI] Fix some docblocks

| Q             | A
| ------------- | ---
| Branch?       | 3.3
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

Commits
-------

a22e839 [DI] Fix some docblocks

src/Symfony/Component/DependencyInjection/ChildDefinition.php

@@ -33,7 +33,7 @@ class ChildDefinition extends Definition
     }
 
     /**
-     * Returns the Definition being decorated.
+     * Returns the Definition to inherit from.
      *
      * @return string
      */
@@ -43,7 +43,7 @@ class ChildDefinition extends Definition
     }
 
     /**
-     * Sets the Definition being decorated.
+     * Sets the Definition to inherit from.
      *
      * @param string $parent
      *

src/Symfony/Component/DependencyInjection/Definition.php

@@ -250,6 +250,14 @@ class Definition
         return $this;
     }
 
+    /**
+     * Sets a specific argument.
+     *
+     * @param int|string $key
+     * @param mixed      $value
+     *
+     * @return $this
+     */
     public function setArgument($key, $value)
     {
         $this->arguments[$key] = $value;
@@ -778,7 +786,7 @@ class Definition
     }
 
     /**
-     * Sets autowired.
+     * Enables/disables autowiring.
      *
      * @param bool $autowired
      *