Add basic README describing Spree installation

framework/spree/README.md

@@ -1,2 +1,49 @@
-TODO: Base README on other Framework READMEs.
-TODO: Link to demo site running NextJS Commerce communicating with Spree.
+# [Spree Commerce][1] Provider
+
+A preview integration of Spree Commerce within NextJS Commerce. It supports browsing and searching Spree products and adding products to the cart as a guest user.
+
+## Installation
+
+Start by following the [instructions for setting up NextJS Commerce][2].
+
+Next, setup Spree. The easiest way to run Spree locally is to follow the installation tutorial available at [the Spree Starter GitHub repository][3].
+
+You may have to adjust Spree Starter to allow `localhost` and [CORS][4] requests. Run `docker-compose run web bundle add rack-cors` and:
+
+```ruby
+# In config/application.rb add a configuration for CORS:
+
+module SpreeStarter
+  class Application < Rails::Application
+    config.middleware.insert_before 0, Rack::Cors do
+      allow do
+        origins '*'
+        resource '*', headers: :any, methods: :any
+      end
+    end
+  end
+end
+
+# In config/environments/development.rb add 'localhost':
+
+config.hosts << 'localhost'
+```
+
+By default, Spree Starter and NextJS Commerce both run on port `3000`. Avoid collisions by running NextJS Commerce on port `4000`:
+
+```json
+// In package.json, modify two scripts:
+{
+  "scripts": {
+    "dev": "NODE_OPTIONS='--inspect' next dev -p 4000",
+    "start": "next start -p 4000",
+    ...
+  }
+  ...
+}
+```
+
+[1]: https://spreecommerce.org/
+[2]: https://github.com/vercel/commerce
+[3]: https://github.com/spree/spree_starter
+[4]: https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS