docs(README): extend the documentation a bit

Author: char0n

README.md

@@ -1,7 +1,25 @@
-# ApiDOM Validator GitHub Actions
+# ApiDOM Validator GitHub Action
 
-This GitHub Actions validates OpenAPI 3.x.y / AsyncAPI 2.x definition file using ApiDOM Language Service.
-The validation is exactly the same as the one that https://editor-next.swagger.io/ uses.
+This GitHub Actions validates [OpenAPI](https://github.com/OAI/OpenAPI-Specification/tree/main/versions) 
+3.x.y / [AsyncAPI](https://github.com/OAI/OpenAPI-Specification/tree/main/versions) 2.x definition file
+using [ApiDOM Language Service](https://github.com/swagger-api/apidom).
+
+Validation rules are exactly the same as the one that https://editor-next.swagger.io/ uses.
+
+**Supported specifications:**
+
+- OpenAPI 3.0.0
+- OpenAPI 3.0.1
+- OpenAPI 3.0.2
+- OpenAPI 3.0.3
+- OpenAPI 3.1.0
+- AsyncAPI 2.0.0
+- AsyncAPI 2.1.0
+- AsyncAPI 2.2.0
+- AsyncAPI 2.3.0
+- AsyncAPI 2.4.0
+- AsyncAPI 2.5.0
+- AsyncAPI 2.6.0
 
 ## Inputs
 
@@ -13,7 +31,7 @@ The validation is exactly the same as the one that https://editor-next.swagger.i
 ## Example usage
 
 ```yaml
-uses: char0n/apidom-validate@master
+uses: char0n/apidom-validate@v1
 with:
   definition-file: 'path/to/my/openapi.yaml'
 ```