Add a changelog file (#33)

Make a guess at the first few of releases and add a fleshed out
`unreleased` section ready for next release.

Author: tcharding

CHANGELOG.md

@@ -0,0 +1,15 @@
+# unreleased
+
+- Add support for Bitcoin Core versions `26.1`, `26.2`, `27.0`, and `27.1` [#21](https://github.com/rust-bitcoin/rust-bitcoind-json-rpc/pull/21)
+- Import `jsonrpc` crate [#19](https://github.com/rust-bitcoin/rust-bitcoind-json-rpc/pull/19)
+- Bump MSRV to Rust `v1.63.0` [#17](https://github.com/rust-bitcoin/rust-bitcoind-json-rpc/pull/17)
+- Migrate repo to `github.com/rust-bitcoin` org (from `github.com/tcharding`).
+
+# 0.3 - June 2024
+
+- Switch from implementing `TryFrom` to implementing inherent `into_model` function [#9](https://github.com/rust-bitcoin/rust-bitcoind-json-rpc/pull/9)
+
+# 0.2 - June 2024
+
+The first two versions were what was needed to get integration testing
+in `rust-miniscript` to be able to use this crate.