minor #11832 Update the PHP requirements for Symfony 3.4 version (javiereguiluz)

This PR was squashed before being merged into the 3.4 branch (closes #11832).

Discussion
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Update the PHP requirements for Symfony 3.4 version

Fixes #11826.

Commits
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882de65 Update the PHP requirements for Symfony 3.4 version

Author: javiereguiluz

reference/requirements.rst

@@ -7,11 +7,15 @@ Requirements for Running Symfony
 ================================
 
 Symfony 3.4 requires **PHP 5.5.9** or higher to run, in addition to other minor
-requirements. To make things simple, Symfony provides a tool to quickly check if
-your system meets all those requirements.
+requirements, when using the traditional installation based on the
+`Symfony Standard Edition`_. If Symfony 3.4 is installed via the `skeleton`_ or
+`website-skeleton`_ (which is the recommended way for modern Symfony
+applications) the requirements are **PHP 7.0.8** or higher.
 
-Beware that PHP can define a different configuration for the command console and
-the web server, so you need to check requirements in both environments.
+To make things simple, Symfony provides a tool to quickly check if your system
+meets all those requirements. Beware that PHP can define a different
+configuration for the command console and the web server, so you need to check
+the requirements in both environments.
 
 Checking Requirements for the Web Server
 ----------------------------------------
@@ -32,3 +36,7 @@ command and fix the reported issues:
 
     $ cd my-project/
     $ php bin/symfony_requirements
+
+.. _`Symfony Standard Edition`: https://github.com/symfony/symfony-standard
+.. _`skeleton`: https://github.com/symfony/skeleton
+.. _`website-skeleton`: https://github.com/symfony/website-skeleton