Document symlinked directories

[g105b]

Something super useful to have is a symlinked directory within www. This allows user uploads to non-www directories, or mounted drives to be served publically.

EDIT: This functionality is now live, but this issue is being kept open while it is documented.

[g105b]

{
	"data/uploads": {
		"require": {
			"vendor/bin/sync": "*"
		},
		"execute": {
			"command": "vendor/bin/sync",
			"arguments": ["--symlink", "data/uploads", "www/data/uploads"]
		}
	},
}

[g105b]

This functionality is tracked in PhpGt/Sync#51, which needs to be completed first.