added composer info

Author: OskarStark

create_framework/http-foundation.rst

@@ -121,6 +121,13 @@ To use this component, add it as a dependency of the project:
 
 Running this command will also automatically download the Symfony
 HttpFoundation component and install it under the ``vendor/`` directory.
+A ``composer.json`` and a ``composer.lock`` file will be generated as well.::
+
+    // composer.json
+    {
+        "require": {
+            "symfony/http-foundation": "^2.7"
+    }
 
 .. sidebar:: Class Autoloading