Clarify that syserr.New must only be called during init

PiperOrigin-RevId: 197599402
Change-Id: I23eb0336195ab0d3e5fb49c0c57fc9e0715a9b75

pkg/syserr/syserr.go

@@ -31,6 +31,8 @@ type Error struct {
 }
 
 // New creates a new Error and adds a translation for it.
+//
+// New must only be called at init.
 func New(message string, linuxTranslation *linux.Errno) *Error {
 	err := &Error{message}
 	linuxABITranslations[err] = linuxTranslation