Cookbook entry for advanced file upload implementation

[jmather]

I think it would be a great addition if we had a cookbook entry that went into greater detail than the current "How to upload files with doctrine" cookbook entry (http://symfony.com/doc/current/cookbook/doctrine/file_uploads.html).

It's great to get people started but we should also be showing people the cleaner way of doing things as well.

[wouterj]

@weaverryan should get a actionable and doc request label.

[jmather]

I think at this point such a cookbook entry should probably just point at the VichUploaderBundle (or be a quick-to-implement and maybe sing-songy description of how to use VichUploaderBundle)

[wouterj]

Closing in favor of #2346
Thnaks for reporting it, we won't forgrt this one intil this doc is fixed