Document the file field crash issue on node 13 (keystonejs#2780)

packages/fields/src/types/File/README.md

@@ -8,6 +8,16 @@ title: File
 
 Support files hosted in a range of different contexts, e.g. in the local filesystem, or on a cloud based file server.
 
+> **Important:** As of this writing (April 2020), an upstream [issue](https://github.com/apollographql/apollo-server/issues/3508) with `apollo-server`'s dependencies can cause a server crash when using this field (regardless of adapter) with **Node 13 only**. To work around this, use Node 12 or below _or_ add the following to your `package.json`:
+>
+> ```js title=package.json
+> "resolutions": {
+>   "graphql-upload": "^10.0.0"
+> }
+> ```
+>
+> You can track this issue [here](https://github.com/keystonejs/keystone/issues/2101).
+
 ## Usage
 
 ```js