docs: add post installation command

docs/pages/installation.md

@@ -16,6 +16,10 @@ allowing users to install and use only the specific components they need for the
 ```shell
 composer require php-flasher/flasher-laravel
 ```
+Then, run:
+```shell
+php artisan flasher:install
+```
 
 <br />
 
@@ -23,6 +27,10 @@ composer require php-flasher/flasher-laravel
 ```shell
 composer require php-flasher/flasher-symfony
 ```
+Then, run:
+```shell
+php bin/console flasher:install
+```
 
 ---