dmesg: add license header.

src/uu/dmesg/src/dmesg.rs

@@ -1,3 +1,8 @@
+// This file is part of the uutils util-linux package.
+//
+// For the full copyright and license information, please view the LICENSE
+// file that was distributed with this source code.
+
 use clap::{crate_version, Arg, ArgAction, Command};
 use regex::Regex;
 use std::fs;

src/uu/dmesg/src/json.rs

@@ -1,3 +1,8 @@
+// This file is part of the uutils util-linux package.
+//
+// For the full copyright and license information, please view the LICENSE
+// file that was distributed with this source code.
+
 use serde::Serialize;
 use std::io;