docs: improve command help

src/main.rs

@@ -14,8 +14,8 @@ use sequoia_openpgp::packet::UserID;
 struct Args {
     /// Filter key fingerprints by using a regular expression.
     ///
-    /// This regex is matched against the hexadecimal representation of the fingerprint, without
-    /// spaces or other additional symbols.
+    /// This regex is matched against the upper-case hexadecimal representation of the fingerprint,
+    /// without spaces or other additional symbols.
     ///
     /// This is implemented using the fancy-regex library: <https://crates.io/crates/fancy-regex>.
     /// You can test and debug your regex here: <https://fancy-regex.github.io/fancy-regex/>.
@@ -27,7 +27,7 @@ struct Args {
     /// By default, status information is only shown if stderr is bound to a terminal and stdout is
     /// *not* bound to a terminal. The latter in particular prevents found keys (which are printed
     /// to stdin) from being "overwritten" by status information printed to stderr.
-    #[arg(long, value_enum, default_value_t)]
+    #[arg(long, value_enum, value_name = "WHEN", default_value_t)]
     status: StatusEnabled,
 
     /// Stop once the specified number of matching keys has been found.