Update doc example

src/lib.rs

@@ -4,11 +4,16 @@
 //! extern crate libnotify;
 //!
 //! fn main() {
-//!    let notify = libnotify::Context::new("hello").unwrap();
+//!     let notify = libnotify::Context::new("hello").unwrap_or_else(|e| {
-//!    let n = notify.new_notification("This is the summary.",
+//!         panic!("{}", e);
-//!                                    Some("This is the optional body text."),
+//!     });
-//!                                    None).unwrap();
+//!     let body_text = Some("This is the optional body text.");
-//!    n.show().unwrap();
+//!     let n = notify.new_notification("This is the summary.",
+//!                                     body_text,
+//!                                     None).unwrap_or_else(|e| {
+//!         panic!("{}", e);
+//!     });
+//!     n.show().ok().expect("Failed to show notification");
 //! }
 //! ```