doc: add minimal example to lib.rs

Author: phip1611

uefi/src/lib.rs

@@ -6,6 +6,21 @@
 //! See the [Rust UEFI Book] for a tutorial, how-tos, and overviews of some
 //! important UEFI concepts. For more details of UEFI, see the latest [UEFI
 //! Specification][spec].
+//! 
+//! # Minimal Example
+//! 
+//! ```ignore
+//! #![no_main]
+//! #![no_std]
+//! use uefi::prelude::*;
+//! 
+//! #[entry]
+//! fn main(_image_handle: Handle, _system_table: SystemTable<Boot>) -> Status {
+//!     uefi::helpers::init().unwrap();
+//!     println!("Hello world!");
+//!     Status::SUCCESS
+//! }
+//! ```
 //!
 //! # Value-add and Use Cases
 //!