types: Improve README

The `types` crate is currently under documented. Improve the
documentation in the crate's readme.

types/README.md

@@ -1,6 +1,35 @@
-# corepc-types
+# Bitcoin Core JSON-RPC types
 
-Types returned by the JSON-RPC API of Bitcoin Core.
+This crate provides data types return by Bitcoin Core's JSON-RPC API. Each type is specific to the
+version of Core e.g., if you run the `getblockchaininfo` method against a Bitcoin Core v28 instance
+you will get back the data described by `types::v28::GetBlockChainInfo`. In a similar fashion any
+method `corerpcmethod` will return type `CoreRpcMethod` - snake-case as is conventional in Rust.
+
+## Status
+
+This crate is Work In Progress - not all methods for all Core versions are done yet. The single
+source of truth (SSOT) for a methods status can be found in the version specific module e.g.,
+`types/src/v17/mod.rs`. The HTML version can be found online and has nice drop down menus.
+
+See for example: https://docs.rs/corepc-types/0.5.0/corepc_types/v18/index.html
+
+### As of `v0.5.0`
+
+- All types to support `rust-miniscript` exist for Core versions 17-28 inclusive. 
+- Support for Core Versions v17 and v18 is more fully fleshed out.
+- Nice docs and `verify` tool for v17 and v18 only.
+
+### Testing and Verification
+
+In order to prove the data structures we do integration testing in `integration_test`. The tests are
+version specific e.g., `carog test --features=0_18_1`. In CI we test against all supported versions.
+If you are using this crate in CI you may want to imitate the job structure. See the `Integration`
+job in `.github/workflows/rust.yaml`.
+
+In order to back up method status our claims we provide the `verify` tool that parses the SSOT and
+checks the claims. Run it using `verify v17` (also `verify all`).
+
+The tool only currently verifies the `v17` and `v18` modules.
 
 ## Minimum Supported Rust Version (MSRV)