add instructions for the release build

BUILDING.md

@@ -204,9 +204,16 @@ Prerequisites: Android Studio with SDK installed
 ... or, to create the `aab` file, `bundle` instead of `build`:
 
    ```bash
-   ./gradlew bundle -Dlint.baselines.continue=true
+   ./gradlew bundleDebug -Dlint.baselines.continue=true
    ```
 
+... or, to create a signed release, add the gradle.properties.secrets file (see properties at top of build.gradle) and the time-safari-upload-key-pkcs12.jks file and `bundleRelease`:
+
+   ```bash
+   ./gradlew bundleRelease -Dlint.baselines.continue=true
+   ```
+
+
 
 ## First-time Android Configuration for deep links