Added Bitcoin Core architecture diagram

ch03.asciidoc

@@ -11,6 +11,13 @@ When bitcoin was created by Satoshi Nakamoto, the software was actually complete
 Even though Bitcoin Core includes a reference implementation of a wallet, this is not intended to be used as a production wallet for users or for applications. Application developers are advised to build wallets using modern standards such as BIP39 and BIP32 (see <<mnemonic_code_words>> and <<hd_wallets>>). BIP stands for _Bitcoin Improvement Proposals_.
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+<<bitcoin_core_architecture>> shows the architecture of Bitcoin Core:
+
+[[bitcoin_core_architecture]]
+.Bitcoin Core Architecture (Source: Eric Lombrozo)
+image::images/mbc2_0301["Bitcoin Core Architecture"]
+
+
 === Bitcoin Development Environment
 
 If you're a developer, you will want to set up a development environment with all the tools, libraries, and support software for writing bitcoin applications. In this highly technical chapter, we'll walk through that process step-by-step. If the material becomes too dense (and you're not actually setting up a development environment) feel free to skip to the next chapter, which is less technical.