Add installation command for Nova v4

Author: alies-dev

README.md

@@ -21,6 +21,11 @@ You can install the package in to a Laravel app that uses [Nova](https://nova.la
 composer require interaction-design-foundation/nova-html-card
 ```
 
+For Nova v4 (Release Candidate):
+```bash
+composer require interaction-design-foundation/nova-html-card ^3.0.0-rc1
+```
+
 
 ## Usage