Update 3.x doc to reflect that whole var dir is writable

[andrerom]

As of 3.0, writeable files are placed in var folder, however the doc for directory permissions does not reflect this other then just mapping the old doc from app => var.

If this is changed to give write access to var it would:

• solve var/sessions write issue introduced in symfony/symfony-standard@dcf4ead
• Make it easier for systems like eZ to add own folder for user uploaded binary files ala asked for in Where to store persistent storage files? #6095 without having to document this specifically for dir permissions (however a convention on this would be nice, so I'm not saying solving this will fully solve it)
• ..

In summary, changing:

$ sudo chmod +a "$HTTPDUSER allow delete,write,append,file_inherit,directory_inherit" var/cache var/logs

to

$ sudo chmod +a "$HTTPDUSER allow delete,write,append,file_inherit,directory_inherit" var

( same goes for all other commands dealing with directory permissions in doc )

[andrerom]

PR: #6136