Add description to composer (#139)

When validating my composer.json file, a warning occurred for this package: "the property description is required".

composer.json

@@ -1,6 +1,7 @@
 {
     "name": "laravel/prompts",
     "type": "library",
+    "description": "Add beautiful and user-friendly forms to your command-line applications.",
     "license": "MIT",
     "autoload": {
         "psr-4": {