Add the description in the composer.json file

./composer.json is valid for simple usage with composer but has
strict errors that make it unable to be published as a package:
See https://getcomposer.org/doc/04-schema.md for details on the schema
description : The property description is required

composer.json

@@ -2,6 +2,7 @@
   "name": "publishpress/publishpress-authors",
   "type": "wordpress-plugin",
   "license": "GPL-2.0-or-later",
+  "description": "",
   "authors": [
     {
       "name": "PublishPress",