Add semver note to documentation (#164)

Author: Sergey-Murtazin

README.md

@@ -21,7 +21,7 @@ The V2 offers:
 
 It will first check the local cache for a version match. If version is not found locally, It will pull it from `main` branch of [go-versions](https://github.com/actions/go-versions/blob/main/versions-manifest.json) repository and on miss or failure, it will fall back to the previous behavior of download directly from [go dist](https://storage.googleapis.com/golang).
 
-Matching by semver spec:
+Matching by [semver spec](https://github.com/npm/node-semver):
 ```yaml
 steps:
   - uses: actions/checkout@v2
@@ -74,6 +74,13 @@ jobs:
       - run: go run hello.go
 ```
 
+### Supported version syntax
+The `go-version` input supports the following syntax:
+
+Specific versions: `1.15`, `1.16.1`, `1.17.0-rc2`, `1.16.0-beta1`  
+SemVer's version range syntax: `^1.13.1`  
+For more information about semantic versioning please refer [semver](https://github.com/npm/node-semver) documentation
+
 # License
 
 The scripts and documentation in this project are released under the [MIT License](LICENSE)