Update platforms docs

* No need to duplicate docs about which is *-latest here.

Author: eregon

README.md

@@ -38,13 +38,13 @@ which means Ruby ≤ 2.4 is unmaintained and considered insecure.
 
 ### Supported Platforms
 
-The action works on these [GitHub-hosted runners](https://help.github.com/en/actions/automating-your-workflow-with-github-actions/virtual-environments-for-github-hosted-runners) virtual environments. Virtual environments not listed below are unsupported.
+The action works on these [GitHub-hosted runners](https://docs.github.com/en/actions/using-github-hosted-runners/about-github-hosted-runners#supported-runners-and-hardware-resources) images. Runner images not listed below are not supported yet. `$OS-latest` just alias to one of these images.
 
-| Operating System | Recommended | Other Supported Versions |
-| ---------------- | ----------- | ------------------------ |
-| Ubuntu  | `ubuntu-latest` (= `ubuntu-22.04`)  | `ubuntu-18.04`, `ubuntu-20.04` |
-| macOS   | `macos-latest` (= `macos-11`)       | `macos-10.15`, `macos-12` |
-| Windows | `windows-latest` (= `windows-2022`) | `windows-2019` |
+| Operating System | Supported |
+| ---------------- | --------- |
+| Ubuntu  | `ubuntu-18.04`, `ubuntu-20.04`, `ubuntu-22.04` |
+| macOS   | `macos-10.15`, `macos-11`, `macos-12` |
+| Windows | `windows-2019`, `windows-2022` |
 
 The prebuilt releases are generated by [ruby-builder](https://github.com/ruby/ruby-builder)
 and on Windows by [RubyInstaller2](https://github.com/oneclick/rubyinstaller2).