minor #1124 Added a note about Symfony 4 and Symfony Skeleton (bocharsky-bw)

This PR was squashed before being merged into the 3.4 branch (closes #1124).

Discussion
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Added a note about Symfony 4 and Symfony Skeleton

Resolve #1121

Commits
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3c9f920 Added a note about Symfony 4 and Symfony Skeleton

Author: fabpot

README.md

@@ -1,6 +1,10 @@
 Symfony Standard Edition
 ========================
 
+**WARNING**: This distribution does not support Symfony 4. See the
+[Installing & Setting up the Symfony Framework][15] page to find a replacement
+that fits you best.
+
 Welcome to the Symfony Standard Edition - a fully-functional Symfony
 application that you can use as the skeleton for your new applications.
 
@@ -70,3 +74,4 @@ Enjoy!
 [11]: https://symfony.com/doc/3.4/logging.html
 [13]: https://symfony.com/doc/current/bundles/SensioGeneratorBundle/index.html
 [14]: https://symfony.com/doc/current/setup/built_in_web_server.html
+[15]: https://symfony.com/doc/current/setup.html