doc: add "About" section

The About section is a more comprehensive write-up of the introduction
sentences at the very beginning. It should guide the user to know what
they can do with this lib.

Author: phip1611

uefi/README.md

@@ -11,6 +11,18 @@ This crate makes it easy to develop Rust software that leverages **safe**,
 ![Build status](https://github.com/rust-osdev/uefi-rs/workflows/Rust/badge.svg)
 ![Stars](https://img.shields.io/github/stars/rust-osdev/uefi-rs)
 
+## About
+
+With `uefi`, you have the flexibility to integrate selected types and
+abstractions into your project or to conveniently create EFI images, addressing
+the entire spectrum of your development needs.
+
+`uefi` works with stable Rust, but additional nightly-only features are
+gated behind an `unstable` Cargo feature flag.
+
+_Note that for producing EFI images, you also need to use a corresponding `uefi`
+compiler target of Rust, such as `x86_64-unknown-uefi`._
+
 For an introduction to the `uefi-rs` project and documentation, please refer to
 our main [README].
 

uefi/src/lib.rs

@@ -7,6 +7,19 @@
 //! important UEFI concepts. For more details of UEFI, see the latest [UEFI
 //! Specification][spec].
 //!
+//! # About `uefi`
+//!
+//! With `uefi`, you have the flexibility to integrate selected types and
+//! abstractions into your project or to conveniently create EFI images,
+//! addressing the entire spectrum of your development needs.
+//!
+//! `uefi` works with stable Rust, but additional nightly-only features are
+//! gated behind an `unstable` Cargo feature flag. Please find more information
+//! about supported features below.
+//!
+//! _Note that for producing EFI images, you also need to use a corresponding
+//! `uefi` compiler target of Rust, such as `x86_64-unknown-uefi`._
+//!
 //! # Interaction with uefi services
 //!
 //! With this crate you can write code for the pre- and post-exit boot services