Merge pull request #40 from rust-lang/help-menu-help-command

Add the ?help command to the help menu

Author: technetos

src/commands.rs

@@ -73,6 +73,7 @@ impl Commands {
     }
 
     pub(crate) fn menu(&mut self) -> Option<String> {
+        self.menu.as_mut().map(|menu| *menu += "?help\n");
         self.menu.take()
     }