container: improve documentation

This change removes inconsistencies collected over time in this package.

Signed-off-by: Ophestra <cat@gensokyo.uk>

container/vfs/mangle.go

@@ -2,6 +2,8 @@ package vfs
 
 import "strings"
 
+// Unmangle reverses mangling of strings done by the kernel. Its behaviour is
+// consistent with the equivalent function in util-linux.
 func Unmangle(s string) string {
 	if !strings.ContainsRune(s, '\\') {
 		return s