feat(book): Add Badges for Crates (#253)

### Description

Small PR to add badges for the crate versions in the book.

book/src/building/engine.md

@@ -1,5 +1,7 @@
 # RPC Engine Types
 
+<a href="https://crates.io/crates/op-alloy-rpc-types-engine"><img src="https://img.shields.io/crates/v/op-alloy-rpc-types-engine.svg" alt="op-alloy-rpc-types-engine crate"></a>
+
 The [`op-alloy-rpc-types-engine`][engine] crate provides Optimism types for interfacing
 with the Engine API in the OP Stack.
 

book/src/building/genesis/README.md

@@ -1,5 +1,7 @@
 # Genesis
 
+<a href="https://crates.io/crates/op-alloy-genesis"><img src="https://img.shields.io/crates/v/op-alloy-genesis.svg" alt="op-alloy-genesis crate"></a>
+
 The genesis crate contains types related to chain genesis.
 
 This section contains in-depth sections on building with [`op-alloy-genesis`][genesis] crate types.

book/src/building/protocol/README.md

@@ -1,5 +1,7 @@
 # Protocol
 
+<a href="https://crates.io/crates/op-alloy-protocol"><img src="https://img.shields.io/crates/v/op-alloy-protocol.svg" alt="op-alloy-protocol crate"></a>
+
 The [`op-alloy-protocol`][protocol] crate contains types, constants, and methods
 specific to Optimism derivation and batch-submission.