Add documentation

README.md

@@ -16,6 +16,7 @@ The V3 edition of the action offers:
 - Proxy support
 - Check latest version
 - Caching packages dependencies
+- stable and olstable aliases
 - Bug Fixes (including issues around version matching and semver)
 
 The action will first check the local cache for a version match. If a version is not found locally, it will pull it from the `main` branch of the [go-versions](https://github.com/actions/go-versions/blob/main/versions-manifest.json) repository. On miss or failure, it will fall back to downloading directly from [go dist](https://storage.googleapis.com/golang). To change the default behavior, please use the [check-latest input](#check-latest-version).
@@ -95,6 +96,31 @@ steps:
       check-latest: true
   - run: go run hello.go
 ```
+
+## stable/oldstable aliases
+
+Given the fact that Go doesn't use semver syntax ranges, and that many Go projects want to run tests based on `stable` and `oldstable` aliases, these aliases are introduced in this action as possible values of the input `go-version`. When alias `stable` is provided, and `check-latest` input is set to `true` action will get the latest stable version from the [`go-versions`](https://github.com/actions/go-versions/blob/main/versions-manifest.json) repository. When `check-latest` is not provided, or set to false, the action will resolve `stable` as the most recent present version from the runners tool cache directory. In case of the `oldstable` alias, if current release is 1.19.x, action will resolve version as 1.18.x, where x is the latest patch release. The `check-latest` rules described above will apply for `oldstable` as well.
+
+```yaml
+steps:
+  - uses: actions/checkout@v3
+  - uses: actions/setup-go@v3
+    with:
+      go-version: 'stable'
+      check-latest: true
+  - run: go run hello.go
+```
+
+```yaml
+steps:
+  - uses: actions/checkout@v3
+  - uses: actions/setup-go@v3
+    with:
+      go-version: 'oldstable'
+      check-latest: true
+  - run: go run hello.go
+```
+
 ## Caching dependency files and build outputs:
 
 The action has a built-in functionality for caching and restoring go modules and build outputs. It uses [actions/cache](https://github.com/actions/cache) under the hood but requires less configuration settings. The `cache` input is optional, and caching is turned off by default.