Document contribution guidelines for API docs

api/README.md

@@ -1,4 +1,4 @@
-# solidus\_api
+# solidus_api
 
 API contains the controllers and rabl views implementing the REST API of Solidus.
 
@@ -12,14 +12,25 @@ bundle exec rspec
 
 ## Documentation
 
-The API documentation is in the [openapi](https://github.com/solidusio/solidus/tree/master/api/openapi)
-directory. It follows the OpenAPI specification and it is hosted on
-[Stoplight](https://solidus.docs.stoplight.io/).
+The API documentation is in the [openapi][docs-dir] directory. It follows the
+OpenAPI specification and it is hosted on [Stoplight Docs][live-docs].
 
-If you want to contribute, you can use [Stoplight Studio](https://stoplight.io/p/studio),
-an OpenAPI editor, to edit the files visually, and copy-paste the 
-resulting code into the `openapi` directory.
+If you want to contribute, you can use [Stoplight Studio][studio]. Simply
+follow these steps:
 
-CircleCI automatically syncs our Git repo with Stoplight when a PR is
-merged, and automatically publishes a new version on Stoplight when
-a new Solidus version is released.
+1. Create a new Stoplight Studio project
+2. Copy-paste the content of `openapi/api.oas2.yml` into your project
+3. Edit the endpoints and models as needed
+4. Copy-paste the result back into `openapi/api.oas2.yml`
+5. Open a PR!
+
+**Note: Only use embedded models in Stoplight Studio, as Stoplight Docs is
+not compatible with externally-defined models!**
+
+CircleCI automatically syncs our Git repo with Stoplight Docs when a PR is
+merged, and automatically publishes a new version on Docs when a new Solidus
+version is released.
+
+[docs-dir]: https://github.com/solidusio/solidus/tree/master/api/openapi
+[live-docs]: https://solidus.docs.stoplight.io
+[studio]: https://stoplight.io/p/studio