Merge pull request #1705 from zcash/readme_crate_summaries

Add crate summaries to README

README.md

@@ -97,6 +97,55 @@ graph TB
     click zcash_spec "https://docs.rs/zcash_spec/" _blank
 ```
 
+### Crates
+
+#### Zcash Protocol
+
+* `zcash_protocol`: Constants & common types
+  - consensus parameters
+  - bounded value types (Zatoshis, ZatBalance)
+  - memo types
+* `zcash_transparent`: Bitcoin-derived transparent transaction components
+  - transparent addresses
+  - transparent input, output, and bundle types
+  - support for transparent parts of pczt construction
+* `zcash_primitives`: Core utilities for working with Zcash transactions
+  - the primary transaction data type
+  - transaction builder(s)
+  - proving, signing, & serialization
+  - low-level fee types
+* `zcash_proofs`: The Sprout circuit & proving system
+
+#### Keys, Addresses & Wallet Support
+
+* `zcash_address`: Parsing & serialization of Zcash addresses
+  - unified address, fvk & ivk containers
+  - no dependencies on protocol-specific types
+  - serialization API definitions
+* `zip321`: Parsing & serizalization for ZIP 321 payment requests
+* `zcash_keys`: Spending Keys, Viewing Keys, & Addresses
+  - protocol-specific & Unified address types
+  - ZIP 32 key & address derivation implementations
+  - Unified spending keys & viewing keys
+  - Sapling spending & viewing key types
+* `pczt`: Data types & interfaces for PCZT construction
+  - partially constructed transaction types
+  - transaction construction role interfaces & partial implementations
+* `zcash_client_backend`: A wallet framework for Zcash
+  - wallet data storage APIs
+  - chain scanning
+  - light client protocol support
+  - fee calculation
+  - transaction proposals & high-level transaction construction APIs
+* `zcash_client_sqlite`: SQLite-based implementation of `zcash_client_backend` storage APIs
+
+#### Utilities & Common Dependencies
+
+* `f4jumble`: Encoding for Unified addresses
+* `zcash_encoding`: Bitcoin-derived transaction encoding utilities for Zcash
+* `equihash`: Proof-of-work protocol implementation
+
+
 ## Security Warnings
 
 These libraries are under development and have not been fully reviewed.