Update gc-installation.md

Author: cdimascio

docs/gc-installation.md

@@ -23,9 +23,17 @@ npm install express-openapi-validator
 yarn add express-openapi-validator
 ```
 
+## OpenAPI 3.1 (support) alpha
+
+_Replace x with the latest alpha version_
+
+```shell
+npm install express-openapi-validator@6.0.0-alpha.<X>
+```
+
 ## Upgrading from 3.x
 
 !!! note 
 
 
-    In v4.x.x, the validator is installed as standard connect middleware using `app.use(...) and/or router.use(...)` ([example](https://github.com/cdimascio/express-openapi-validator/blob/v4/README.md#Example-Express-API-Server)). This differs from the v3.x.x the installation which required the `install` method(s). The `install` methods no longer exist in v4.
+    In v4.x.x, the validator is installed as standard connect middleware using `app.use(...) and/or router.use(...)` ([example](https://github.com/cdimascio/express-openapi-validator/blob/v4/README.md#Example-Express-API-Server)). This differs from the v3.x.x the installation which required the `install` method(s). The `install` methods no longer exist in v4.