message: (docs) - Add note about third argument in readFragment
diff: @@ -300,6 +300,23 @@ cache.readFragment(
  Note that the `__typename` may be left out on the partial entity, since the `__typename` is already
  present on the fragment itself.
  +If any fields on the fragment require variables, you can pass them as the third argument like so:
  +
  +```js
  +import gql from 'graphql-tag';
  +
  +cache.readFragment(
  + gql`
  + fragment _ on User {
  + id
  + permissions(byGroupId: $groupId)
  + }
  + `,
  + { id: 1 }, // this identifies the fragment (User) entity
  + { groupId: 5 } // any additional field variables
  +)
  +```
  +
  [Read more about using `readFragment` on the ["Computed Queries"
  page.](../graphcache/computed-queries.md#reading-a-fragment)
  