Update GraphQL release notes for 2.3.4 (#6409)

* Add 2.3.4 features to GraphQL release notes

* Add Community contributions

* review comments + add links

Author: keharper

src/guides/v2.3/graphql/release-notes.md

@@ -3,7 +3,7 @@ group: graphql
 title: Release Notes
 ---
 
-*Release notes published October 2019.*
+*Release notes published January 2020.*
 
 GraphQL is a flexible and performant API that allows you to build custom front-ends, including headless storefronts, [Progressive Web Apps](https://github.com/magento/pwa-studio) (PWA), and mobile apps for Magento.
 
@@ -15,6 +15,25 @@ These release notes can include:
 -  {:.new}New features
 -  {:.fix}Fixes and improvements
 
+## {{site.data.var.ee}} and {{site.data.var.ce}} 2.3.4
+
+-  {:.new} **Guest carts can now be merged with customer carts.** The [`mergeCarts`]({{page.baseurl}}/graphql/mutations/merge-carts.html) mutation transfers the contents of a guest cart into the cart of a logged-in customer.
+-  {:.new} **A customer can start an order on one device and complete it on another.** Use the [`customerCart]({{page.baseurl}}/graphql/queries/customer-cart.html) query to obtain the cart ID for a logged-in customer.
+-  {:.new} **Layered navigation can use custom filters.** The `filter` attribute of the [`products`]({{page.baseurl}}/graphql/queries/products.html) query now requires the `ProductAttributeFilterInput` object. You can specify a pre-defined filter in this object, or [define a custom filter]({{page.baseurl}}/graphql/custom-filters.html). As a result, layered navigation on your website filters on the attributes you need.
+-  {:.new} **You can search categories by ID, name, and/or URL key.** The [`categoryList`]({{page.baseurl}}/graphql/queries/category-list.html) query replaces the deprecated `category` query.
+-  {:.new} **A customer can add bundle and downloadable products to the cart with the [`addBundleProductsToCart`]({{page.baseurl}}/graphql/mutations/add-bundle-products.html) and [`addDownloadableProductsToCart`]({{page.baseurl}}/graphql/mutations/add-downloadable-products.html) mutations.**
+-  {:.new} **The [`ProductInterface`]({{page.baseurl}}/graphql/product/product-interface.html) supports fixed product taxes (such as WEEE).** Use the [`storeConfig`]({{page.baseurl}}/graphql/queries/store-config.html) query to determine whether the store supports these taxes.
+-  {:.new} **The [`cart`]({{page.baseurl}}/graphql/queries/cart.html) object has been enhanced to include information about promotions and applied discounts at the line and cart levels.**
+-  {:.new} **Added test coverage in multiple GraphQL modules.**
+
+The following queries and mutations have been deprecated:
+
+Deprecated entity | Use this instead
+--- | ---
+`category` query | `categoryList` query
+`setPaymentMethodOnCartAndPlaceOrder` mutation | Run the `setPaymentMethodOnCart` and `placeOrder` mutations in the same request
+`wishlist` query | `customer` query
+
 ## {{site.data.var.ee}} and {{site.data.var.ce}} 2.3.3
 
 -  {:.new} **GraphQL supports PayPal, Braintree, and Authorize.Net payment methods.** You can use mutations to set the payment method, retrieve payment method-specific tokens, and place an order. For details, see the following topics: