title: set firestore security rule without auth
body: <p>im building an ecommerce app , without AUTH or payment method (pay when u receive the item) ... so i will set the fav and bascket item in local storage (react native )
  and for the order ,the user add it in firestore document (order doc)
  i have two doc product and order
  so i want to set my firestore security rule to allow read from product doc
  and only write for order doc
  and is it safe to do it like that</p>
  <pre><code>rules_version = '2';
  service cloud.firestore {
    match /databases/{database}/documents {
      match /{document=**} {
        allow read, write
      }
    }
  }
  </code></pre>