minor #12760 Update setup.rst (rsaylor73)

This PR was submitted for the 4.4 branch but it was merged into the 4.3 branch instead (closes #12760).

Discussion
----------

Update setup.rst

<!--

If your pull request fixes a BUG, use the oldest maintained branch that contains
the bug (see https://symfony.com/roadmap for the list of maintained branches).

If your pull request documents a NEW FEATURE, use the same Symfony branch where
the feature was introduced (and `master` for features of unreleased versions).

-->

Commits
-------

e0f0908 Update setup.rst

Author: javiereguiluz

setup.rst

@@ -61,6 +61,10 @@ commands to create the new Symfony application using Composer:
 
     # run this if you are building a microservice, console application or API
     $ composer create-project symfony/skeleton my_project_name
+    
+    # to specify the version of Symfony to install
+    $ composer create-project symfony/website-skeleton:^4.x my_project_name
+    Replace 4.x with the version. IE: 4.4
 
 No matter which command you run to create the Symfony application. All of them
 will create a new ``my_project_name/`` directory, download some dependencies