Add windows-2016 to supported platforms

* Recommend to use *-latest.

README.md

@@ -33,13 +33,13 @@ On Windows, Ruby 2.4 uses OpenSSL 1.0.2, which is no longer maintained.
 
 The action works for all [GitHub-hosted runners](https://help.github.com/en/actions/automating-your-workflow-with-github-actions/virtual-environments-for-github-hosted-runners).
 
-| Operating System | Versions |
-| ----------- | -------- |
-| Ubuntu  | `ubuntu-20.04`, `ubuntu-latest` (= `ubuntu-18.04`), `ubuntu-16.04` |
-| macOS   | `macos-latest` |
-| Windows | `windows-latest` |
+| Operating System | Recommended | Other Supported Versions |
+| ----------- | -------- | -------- |
+| Ubuntu  | `ubuntu-latest`  (= `ubuntu-18.04`) | `ubuntu-20.04`, `ubuntu-16.04` |
+| macOS   | `macos-latest`   (= `macos-10.15`)  | |
+| Windows | `windows-latest` (= `windows-2019`) | `windows-2016` |
 
-Rubinius is only available on `ubuntu-latest`.
+Rubinius is only available on `ubuntu-18.04`.
 
 The prebuilt releases are generated by [ruby-builder](https://github.com/ruby/ruby-builder)
 and on Windows by [RubyInstaller2](https://github.com/oneclick/rubyinstaller2).