validate specific vendor README update

README.md

@@ -71,6 +71,12 @@ To validate data:
 $ make validate
 ```
 
+The validation also supports validating a single vendor's files:
+
+```bash
+$ make validate vendor-id=<id-of-vendor>
+```
+
 [Visual Studio Code](https://code.visualstudio.com/) is a great editor for editing the Device Repository. You can validate your data automatically using the [YAML plugin](https://marketplace.visualstudio.com/items?itemName=redhat.vscode-yaml).
 
 The YAML plugin supports you with filling out the document. When hitting Ctrl + Space, all fields are shown. The Debug Console of Visual Studio provides feedback by highlighting the incorrect fields.