Update --help output

- More detailed and polished.

crates/popcorn/src/args.rs

@@ -1,15 +1,39 @@
-use clap::Parser;
+use clap::{Parser, ValueHint};
 
 #[derive(Parser, Debug)]
-#[command(name = "popcorn", version, about = "Minimal OSD popup renderer")]
+#[command(
+    name = "popcorn",
+    version,
+    about = "Minimal OSD popup renderer",
+    long_about = "Minimal, configurable on-screen display popup.\n\
+                  Called by other programs or keybindings to show volume, brightness, and battery level popups."
+)]
 pub struct CliArgs {
-    #[arg(long = "value")]
+    /// Percentage value to display (0 to 100). Usually volume or brightness.
+    #[arg(
+        long = "value",
+        value_name = "PERCENT",
+        help = "Percentage value for the OSD (0 to 100)",
+        value_hint = ValueHint::Other
+    )]
     pub value: Option<u8>,
 
-    #[arg(long = "icon")]
+    /// Icon glyph to display. Usually provided by a Nerd Font.
+    #[arg(
+        long = "icon",
+        value_name = "GLYPH",
+        help = "Icon glyph (UTF-8). If omitted, config default is used",
+        value_hint = ValueHint::Other
+    )]
     pub icon: Option<String>,
 
-    #[arg(long = "color")]
+    /// Fill color in AARRGGBB hex format.
+    #[arg(
+        long = "color",
+        value_name = "AARRGGBB",
+        help = "Fill color in hex (AARRGGBB). If omitted, config default is used",
+        value_hint = ValueHint::Other
+    )]
     pub color: Option<String>,
 }