add android instructions in readme

README.md

@@ -9,10 +9,50 @@
 
 </div>
 
+## Setup
+
+HCB Mobile connects to HCB throught the v4 API.
+You can either do this on the production HCB instance, or using a local development instance.
+
+### Production HCB
+
+Set your `.env` to include the following variables:
+
+```
+EXPO_PUBLIC_API_BASE=https://hcb.hackclub.com/api/v4
+EXPO_PUBLIC_CLIENT_ID=yt8JHmPDmmYYLUmoEiGtocYwg5fSOGCrcIY3G-vkMRs
+EXPO_PUBLIC_STRIPE_API_KEY=pk_live_UAjIP1Kss29XZ6tW0MFWkjUQ
+```
+
+### Development HCB
+
+Go into the Rails console on your development server (`bin/rails c`), and run the following:
+
+```
+app = Doorkeeper::Application.create(name: "mobile", redirect_uri: "hcb://", scopes: ["read", "write"], confidential: false)
+```
+
+Then, set your `.env` to include the following variables:
+
+```
+EXPO_PUBLIC_API_BASE=http://<host>/api/v4
+EXPO_PUBLIC_CLIENT_ID=<uid field from the Doorkeeper app>
+```
+
 ## Building on iOS
 
 1. Install Xcode/Node.js
 2. `npm install`
 3. `npm run ios` - builds and runs the app in a simulator
-   - Run with the `--device` flag to get a device selector, e.g. to run on a physical iPhone
+   - Run with the `-- --device` flag to get a device selector, e.g. to run on a physical iPhone
    - Bonus task: fry an egg on your Mac while this runs
+
+## Building on Android
+
+1. Install Android Studio & Node.js
+2. Setup a new AVD in Android Studio with api >= 34
+3. Install & set your `JAVA_HOME` to a Java 17 SDK
+4. `npm install`
+5. `npm run android` - builds and runs the app in a simulator
+   - Run with the `-- --device` flag to get a device selector, e.g. to run on a physical Android phone
+   - Bonus task: painfully watch Gradle attempt to work