feature: Support for dereference links -L follow

du has -L flag which allows it to dereference or follow
symlinks. Clone this feature into dust.
https://github.com/bootandy/dust/issues/276

src/cli.rs

@@ -33,6 +33,12 @@ pub fn build_cli() -> Command<'static> {
                 .number_of_values(1)
                 .multiple_occurrences(true)
                 .help("Exclude any file or directory with this name"),
+        )
+         .arg(
+            Arg::new("dereference_links")
+                .short('L')
+                .long("dereference-links")
+                .help("dereference sym links - Treat sym links as directories and go into them"),
         )
         .arg(
             Arg::new("limit_filesystem")
@@ -136,6 +142,6 @@ pub fn build_cli() -> Command<'static> {
             Arg::new("only_dir")
                 .short('D')
                 .long("only-dir")
-                .help("Only directories will be displayed."), 
+                .help("Only directories will be displayed."),
         )
 }