Docs: Improved the package description.

package.json

 {
   "name": "@ckeditor/ckeditor5-build-decoupled-document",
   "version": "10.1.0",
-  "description": "CKEditor 5 document editor build.",
+  "description": "The document editor build of CKEditor 5 – the best browser-based rich text editor.",
   "keywords": [
     "ckeditor5-build",
     "CKEditor",