minor #5963 Add note about 'phar extension' dependency (snoek09)

This PR was squashed before being merged into the 2.3 branch (closes #5963).

Discussion
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Add note about 'phar extension' dependency

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | all
| Fixed tickets | #5919

Commits
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696c154 Add note about 'phar extension' dependency

Author: wouterj

best_practices/creating-the-project.rst

@@ -25,6 +25,11 @@ Now that everything is correctly set up, you can create a new project based on
 Symfony. In your command console, browse to a directory where you have permission
 to create files and execute the following commands:
 
+.. note::
+
+    If the installer doesn't work for you or doesn't output anything, make sure
+    that the `phar extension`_ is installed and enabled on your computer.
+
 .. code-block:: bash
 
     # Linux, Mac OS X
@@ -178,3 +183,4 @@ the Symfony directory structure.
 .. _`Composer download page`: https://getcomposer.org/download/
 .. _`public checksums repository`: https://github.com/sensiolabs/checksums
 .. _`these steps`: http://fabien.potencier.org/signing-project-releases.html
+.. _`phar extension`: http://php.net/manual/en/intro.phar.php