Document that the cookie passed to ResponseHeader.SetCookie may be re-used after the function returns

header.go

@@ -946,6 +946,8 @@ func (h *ResponseHeader) SetCanonical(key, value []byte) {
 }
 
 // SetCookie sets the given response cookie.
+//
+// It is save re-using the cookie after the function returns.
 func (h *ResponseHeader) SetCookie(cookie *Cookie) {
 	h.cookies = setArgBytes(h.cookies, cookie.Key(), cookie.Cookie())
 }