chore: add build step to README (#52)

Author: wenfix

README.md

@@ -10,10 +10,10 @@ Follow these steps to run the full end-to-end demo on your machine.
 
 ### Prerequisites
 
-*   **Node.js**: Use version 18.x or later.
-*   **Yarn**: This repository uses Yarn for package management.
-*   **Docker & Docker Compose**: Required to run the backend relay server.
-*   **Expo Go App**: To run the mobile wallet demo, you'll need the [Expo Go](https://expo.dev/go) app on your iOS or Android device.
+- **Node.js**: Use version 18.x or later.
+- **Yarn**: This repository uses Yarn for package management.
+- **Docker & Docker Compose**: Required to run the backend relay server.
+- **Expo Go App**: To run the mobile wallet demo, you'll need the [Expo Go](https://expo.dev/go) app on your iOS or Android device.
 
 ### 1. Installation
 
@@ -25,6 +25,12 @@ cd mobile-wallet-protocol
 yarn install
 ```
 
+To use the demo apps locally you also have to build the packages.
+
+```bash
+yarn build
+```
+
 ### 2. Run the Backend Relay Server
 
 The relay server runs in a Docker container. Use the provided Docker Compose file to start it.
@@ -122,4 +128,4 @@ To work around this, the `yarn release` command executes a wrapper script (`scri
 3.  **Restores and Updates `package.json`**: After the release tool completes, the script reads the new version number. It then restores the original `package.json` contents from the backup and updates its version to match the new release version.
 4.  **Finalizes the Release**: Finally, the script removes the backup file and runs `yarn install` and `yarn lint:fix` to ensure the project is in a consistent state.
 
-This approach ensures that our development workflow, which relies on Yarn workspaces to link the demo apps with local packages, remains unbroken, while also producing a clean and correct release.
+This approach ensures that our development workflow, which relies on Yarn workspaces to link the demo apps with local packages, remains unbroken, while also producing a clean and correct release.