move os_release module to src root, it isn't related to Files

src/main.rs

@@ -5,6 +5,7 @@ mod config;
 mod dirs;
 mod error;
 mod files;
+mod os_release;
 mod skel;
 mod util;
 
@@ -38,7 +39,7 @@ fn main() -> error::MkrootResult<()> {
 	d.push("lib64");
 	files::Files::set_linker_permissions(&files.lib64s, &d, config.verbose)?;
 
-	if let Err(e) = files::os_release(&config) {
+	if let Err(e) = os_release::os_release(&config) {
 		return Err(error::MkrootError::from(format!(
 			"Error creating etc/os-release: {}",
 			e