doc: add minimal example to lib.rs

Author: phip1611

uefi/src/lib.rs

@@ -7,6 +7,26 @@
 //! important UEFI concepts. For more details of UEFI, see the latest [UEFI
 //! Specification][spec].
 //!
+//! # Minimal Example
+//!
+//! Minimal example for an UEFI application using functionality of the
+//! `uefi` crate:
+//!
+//! ```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
+//! }
+//! ```
+//!
+//! Please find more info in our [Rust UEFI Book].
+//!
 //! # Value-add and Use Cases
 //!
 //! `uefi` supports writing code for both pre- and post-exit boot services