Add program description to full help

src/help.rs

@@ -110,6 +110,11 @@ impl<ID> core::fmt::Display for StandardFullHelpWriter<'_, ID> {
     }
     writeln!(f)?;
 
+    if let Some(description) = self.0.options.description {
+      writeln!(f)?;
+      writeln!(f, "{description}")?;
+    }
+
     fn calculate_left_pad<ID: 'static>(option: &Opt<ID>) -> usize {
       (match option.names {
         OptIdentifier::Single(name) => name.chars().count(),

src/options.rs

@@ -5,16 +5,22 @@
 
 /// Static structure that contains instructions for parsing command-line arguments
 pub struct Opts<ID: 'static> {
-  /// String containing single characters that match option prefixes
-  flag_chars: &'static str,
   /// List of options
   options: &'static[Opt<ID>],
+  /// String containing single characters that match option prefixes
+  flag_chars: &'static str,
+  /// A description of what the program does
+  description: Option<&'static str>,
 }
 
 impl<ID: 'static> Opts<ID> {
   /// Build argument parser options with the default flag character of '-'
   pub const fn new(options: &'static[Opt<ID>]) -> Self {
-    Self { flag_chars: "-", options }
+    Self {
+      options,
+      flag_chars: "-",
+      description: None,
+    }
   }
 
   /// Set the recognised flag/option characters.
@@ -22,4 +28,10 @@ impl<ID: 'static> Opts<ID> {
     self.flag_chars = flag_chars;
     self
   }
+
+  /// Set the description of the program, available to help writers.
+  pub const fn with_description(mut self, description: &'static str) -> Self {
+    self.description = Some(description);
+    self
+  }
 }