Update structops comments

src/main.rs

@@ -96,7 +96,7 @@ fn make_spinner(msg: &'static str, done_msg: &'static str) -> ProgressBar {
 
 #[derive(StructOpt)]
 struct Opt {
-    /// The image to turn into a mosaic
+    /// The image path to turn cover images into mosaics
     #[structopt(short, long, parse(from_os_str))]
     input_dir: PathBuf,
 
@@ -104,15 +104,17 @@ struct Opt {
     #[structopt(short, long, parse(from_os_str))]
     tiles_dir: PathBuf,
 
-    /// Where to save the finished mosaic
+    /// Where to save the finished mosaic images
     #[structopt(short, long, parse(from_os_str), default_value = "output")]
     output_dir: PathBuf,
 
-    /// The side length that the target image'll be resized to.
+    /// The side length that the target image will be resized to.
+    /// A mosaic will consist of mosaic_size x mosaic_size tiles.
     #[structopt(short, long, default_value = "128")]
     mosaic_size: u32,
 
     /// The side length of each tile.
+    /// This influences the image resolution inside a tile.
     #[structopt(long, default_value = "26")]
     tile_size: u32,