doc: add "About" section

The About section is a more comprehensive write-up of the TL;DR section
mentioned earlier. It should guide the user to know what they can do with
this lib.

Author: phip1611

uefi/README.md

@@ -13,6 +13,18 @@ Rusty wrapper for the [Unified Extensible Firmware Interface][UEFI].
 Develop Rust software that leverages **safe**, **convenient**, and
 **performant** abstractions for [UEFI] functionality.
 
+## 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

@@ -16,6 +16,19 @@
 //! as general information about the project, such as license or MSRV
 //! requirements.
 //!
+//! # 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