minor #15543 [FrameworkBundle] add a suggest for the serializer component (lsmith77)

This PR was submitted for the 2.7 branch but it was merged into the 2.3 branch instead (closes #15543).

Discussion
----------

[FrameworkBundle] add a suggest for the serializer component

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | -
| Fixed tickets | failing .. but due to unrelated issues in the 2.7 branch
| License       | MIT
| Doc PR        | -

Commits
-------

c7acde8 [FrameworkBundle] add a suggest for the serializer component

src/Symfony/Bundle/FrameworkBundle/composer.json

@@ -45,10 +45,11 @@
         "symfony/yaml": "~2.0,>=2.0.5"
     },
     "suggest": {
-        "symfony/console": "",
-        "symfony/finder": "",
-        "symfony/form": "",
-        "symfony/validator": ""
+        "symfony/console": "For using the console commands",
+        "symfony/finder": "For using the translation loader and cache warmer",
+        "symfony/form": "For using forms",
+        "symfony/validator": "For using validation",
+        "symfony/serializer": "For using the serializer service",
     },
     "autoload": {
         "psr-0": { "Symfony\\Bundle\\FrameworkBundle\\": "" }