docs(CONTRIBUTING.md): improve instructions for upgrading config plugins to newer Expo versions

Author: hassankhan

CONTRIBUTING.md

@@ -26,7 +26,10 @@ Be sure to run the following scripts in the **root directory** to update automat
 
 - Ensure every project under `apps/` is updated to latest version of Expo
 - Ensure every library under `packages/` has a peer dependency on the same version of Expo
-- Update each library’s `README.md` for the same version of Expo
+- Update each library’s `README.md`
+  - Ensuring the latest version of Expo is listed
+  - Ensure the upstream package version is correct
+  - Use the next version for the matching config plugin
 - Update `SDK_VERSION` in [`scripts/generate-plugin.ts`](https://github.com/expo/config-plugins/blob/566f54e785147d88cb4c98490c3e536ee7ef3001/scripts/generate-plugin.ts#L67)
 
 ## Publishing a release