Add mention of changelog in README

Author: arp242

README.md

@@ -10,6 +10,10 @@ Compatible with TOML version [v1.0.0](https://toml.io/en/v1.0.0).
 
 Documentation: https://godocs.io/github.com/BurntSushi/toml
 
+See the [releases page](https://github.com/BurntSushi/toml/releases) for a
+changelog; this information is also in the git tag annotations (e.g. `git show
+v0.4.0`).
+
 This library requires Go 1.13 or newer; install it with:
 
     $ go get github.com/BurntSushi/toml