[Best Practices] Symfony installer

[michaelcullum]

At present it discusses using composer's create-project command then php app/check.php whereas I believe moving over to using the symfony installer would be considered a better practice now that it exists?

[stof]

This is the goal once the installer is ready. Currently, it still has some annoying bugs

[javiereguiluz]

@michaelcullum thanks for your suggestion. This issue is being discussed in this other PR: #4580

[wouterj]

This is now fixed by #4580

Thanks for reporting it!