add link to Architecture & Making a Plugin

README.md

@@ -99,7 +99,7 @@ Alternatively, you can also use a pre-built bundle from Transloadit's CDN: Edgly
 - [Plugins](https://uppy.io/docs/plugins/) — list of Uppy plugins and their options.
 - [Server](https://uppy.io/docs/server/) — setting up and running an Uppy Server instance, which adds support for Instagram, Dropbox, Google Drive and other remote sources.
 - [React](https://uppy.io/docs/react/) — components to integrate Uppy UI plugins with React apps.
-- Architecture & Making a Plugin — how to write a plugin for Uppy [documentation in progress].
+- [Architecture & Making a Plugin](https://uppy.io/docs/writing-plugins/) — how to write a plugin for Uppy [documentation in progress].
 
 ## Plugins