book: Add light client section

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

subxt/src/book/usage/light_client.rs

@@ -0,0 +1,39 @@
+// Copyright 2019-2023 Parity Technologies (UK) Ltd.
+// This file is dual-licensed as Apache-2.0 or GPL-3.0.
+// see LICENSE for license details.
+
+//! # Light Clien
+//!
+//! The light client vision is to help the decentralization of blockchains.
+//! They connect to the p2p network, behaving similarly to a full node without needing excessive synchronization.
+//!
+//! The `unstable-light-client` feature flag enables this functionality.
+//!
+//! To connect to a blockchain network, the light client requires a trusted sync state of the network.
+//!
+//! ```bash
+//! {
+//!    "bootNodes": [
+//!      "/ip4/127.0.0.1/tcp/30333/p2p/12D3KooWEyoppNCUx8Yx66oV9fJnriXwCcXwDDUA2kj6vnc6iDEp"
+//!    ],
+//!    "genesis": { ... },
+//! }
+//! ```
+//!
+//! ## Example
+//!
+//! Here's an example which connects to a local chain and submits a transaction:
+//!
+//! ```rust,ignore
+#![doc = include_str!("../../../../examples/examples/unstable_light_client_tx_basic.rs")]
+//! ```
+//!
+//! ## Example live chain
+//!
+//! The following example connects to the polkadot live chain and performs
+//! several queries using the light client.
+//!
+//! ```rust,ignore
+#![doc = include_str!("../../../../examples/examples/unstable_light_client.rs")]
+//! ```
+//!

subxt/src/book/usage/mod.rs

@@ -10,12 +10,14 @@
 //! - [Constants](constants)
 //! - [Blocks](blocks)
 //! - [Runtime APIs](runtime_apis)
+//! - [Unstable Light Client](light_client)
 //!
 //! Alternately, [go back](super).
 
 pub mod blocks;
 pub mod constants;
 pub mod events;
+pub mod light_client;
 pub mod runtime_apis;
 pub mod storage;
 pub mod transactions;