Add mobile upload example (#13799)

Author: dylanjeffers

packages/mobile/examples/upload/.env.example

@@ -0,0 +1,8 @@
+# Same API key as server — so OAuth connects the user to your developer app
+EXPO_PUBLIC_AUDIUS_API_KEY=
+
+# URL of the upload server (run server first).
+# iOS simulator: http://localhost:3003
+# Android emulator: http://10.0.2.2:3003
+# Physical device: use your computer's LAN IP, e.g. http://192.168.4.107:3003
+EXPO_PUBLIC_WRITE_SERVER_URL=http://localhost:3003

packages/mobile/examples/upload/.expo/README.md

@@ -0,0 +1,13 @@
+> Why do I have a folder named ".expo" in my project?
+
+The ".expo" folder is created when an Expo project is started using "expo start" command.
+
+> What do the files contain?
+
+- "devices.json": contains information about devices that have recently opened this project. This is used to populate the "Development sessions" list in your development builds.
+- "settings.json": contains the server configuration that is used to serve the application manifest.
+
+> Should I commit the ".expo" folder?
+
+No, you should not share the ".expo" folder. It does not contain any information that is relevant for other developers working on the project, it is specific to your machine.
+Upon project creation, the ".expo" folder is already added to your ".gitignore" file.

packages/mobile/examples/upload/.expo/devices.json

@@ -0,0 +1,3 @@
+{
+  "devices": []
+}

packages/mobile/examples/upload/.gitignore

@@ -0,0 +1,3 @@
+.env
+.env.local
+node_modules