Add changelog/releases info

[epelc]

It would be nice if the project used the github Releases feature or added a changelog.md file.

Right now there are only tags with version numbers but no info. This helps people evaluating new libs and users of a lib know when it's safe to upgrade or what might have changed.

[alexcrichton]

I agree it would be good to maintain this! In the meantime you can read over Wasmtime's release notes which are a rough proxy for this module too.