Merge bitcoindevkit/bdk#554: Fix hierarchy of headers on docs landing page

364ad95e85 Fix hierarchy of headers on docs landing page (thunderbiscuit)

Pull request description:

  ### Description

  This PR fixes the hierarchy of headers on the lib.rs docs. I noticed it as I was reading through the docs. The new hierarchy is the following:

  - About (h1)
  - A tour of BDK (h1)
  - Examples (h1)
    - Sync the balance of a descriptor (h2)
    - Generate a few addresses (h2)
    - Create a transaction (h2)
    - Sign a transaction (h2)
  - Feature flags (h1)
  - Internal features (h1)

  ### Checklists

  #### All Submissions:

  * [x] I've signed all my commits
  * [x] I followed the [contribution guidelines](https://github.com/bitcoindevkit/bdk/blob/master/CONTRIBUTING.md)
  * [x] I ran `cargo fmt` and `cargo clippy` before committing

ACKs for top commit:
  rajarshimaitra:
    tACK 364ad95e85

Tree-SHA512: b4439a200c320a1815c572ac36b81c4d684209cb5cf1b90d3f761893ad672a270722be7d7b61d77434a7f98c4276d6fc9694d0c86cacf03c72dc35ca17b5e7d3

src/lib.rs

@@ -46,12 +46,13 @@
 //! ```toml
 //! bdk = "0.17.0"
 //! ```
+//!
+//! # Examples
 #![cfg_attr(
     feature = "electrum",
     doc = r##"
 ## Sync the balance of a descriptor
 
-### Example
 ```no_run
 use bdk::{Wallet, SyncOptions};
 use bdk::database::MemoryDatabase;
@@ -80,7 +81,6 @@ fn main() -> Result<(), bdk::Error> {
 //!
 //! ## Generate a few addresses
 //!
-//! ### Example
 //! ```
 //! use bdk::{Wallet};
 //! use bdk::database::MemoryDatabase;
@@ -106,7 +106,6 @@ fn main() -> Result<(), bdk::Error> {
     doc = r##"
 ## Create a transaction
 
-### Example
 ```no_run
 use bdk::{FeeRate, Wallet, SyncOptions};
 use bdk::database::MemoryDatabase;
@@ -150,7 +149,6 @@ fn main() -> Result<(), bdk::Error> {
 //!
 //! ## Sign a transaction
 //!
-//! ### Example
 //! ```no_run
 //! use std::str::FromStr;
 //!
@@ -192,7 +190,7 @@ fn main() -> Result<(), bdk::Error> {
 //! * `async-interface`: async functions in bdk traits
 //! * `keys-bip39`: [BIP-39](https://github.com/bitcoin/bips/blob/master/bip-0039.mediawiki) mnemonic codes for generating deterministic keys
 //!
-//! ## Internal features
+//! # Internal features
 //!
 //! These features do not expose any new API, but influence internal implementation aspects of
 //! BDK.