mktemp: move help strings to markdown file

src/uu/mktemp/mktemp.md

@@ -0,0 +1,7 @@
+# mktemp
+
+```
+mktemp [OPTION]... [TEMPLATE]
+```
+
+Create a temporary file or directory.

src/uu/mktemp/src/mktemp.rs

@@ -11,7 +11,7 @@
 use clap::{crate_version, Arg, ArgAction, ArgMatches, Command};
 use uucore::display::{println_verbatim, Quotable};
 use uucore::error::{FromIo, UError, UResult, UUsageError};
-use uucore::format_usage;
+use uucore::{format_usage, help_about, help_usage};
 
 use std::env;
 use std::error::Error;
@@ -28,8 +28,8 @@ use std::os::unix::prelude::PermissionsExt;
 use rand::Rng;
 use tempfile::Builder;
 
-static ABOUT: &str = "Create a temporary file or directory.";
-const USAGE: &str = "{} [OPTION]... [TEMPLATE]";
+const ABOUT: &str = help_about!("mktemp.md");
+const USAGE: &str = help_usage!("mktemp.md");
 
 static DEFAULT_TEMPLATE: &str = "tmp.XXXXXXXXXX";