[Docs] Add "Upload files via GraphQL" feature

README.md

@@ -97,6 +97,10 @@ You can easily add a query (or fragment) you see in the documentation into the e
 
 ![add fragment](src/assets/img/readme/add-fragment.gif "Altair GraphQL Client")
 
+### Upload files via GraphQL
+
+You can use binary files as variables to upload them via GraphQL to server (if it implemented the [GraphQL multipart request specification](https://github.com/jaydenseric/graphql-multipart-request-spec)).
+
 ### Autocompletion of fields, arguments, types, etc
 
 You get an autocomplete list of valid terms you can use as you type out your query in the editor.
@@ -236,4 +240,4 @@ Thanks goes to these wonderful people ([emoji key](https://github.com/all-contri
 | :---: | :---: | :---: | :---: |
 <!-- ALL-CONTRIBUTORS-LIST:END -->
 
-This project follows the [all-contributors](https://github.com/all-contributors/all-contributors) specification. Contributions of any kind welcome!
+This project follows the [all-contributors](https://github.com/all-contributors/all-contributors) specification. Contributions of any kind welcome!