updated gesture recognizer readme

examples/gesture_recognizer/android/README.md

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-placeholder README.md
+
+# MediaPipe Tasks Gesture Recognizer Android Demo
+
+### Overview
+
+This is a camera app that continuously detects hand landmarks and classifies gestures (gesture name and confidence level) in the frames seen by your device's back camera using a custom [**task**](https://storage.googleapis.com/mediapipe-assets/gesture_recognizer.task) file.
+
+The task file is downloaded by a Gradle script when you build and run the app. You don't need to do any additional steps to download task files into the project explicitly unless you wish to use your own custom gesture recognition task. If you do use your own task file, place it into the app's *assets* directory.
+
+This application should be run on a physical Android device to take advantage of the physical camera.
+
+## Build the demo using Android Studio
+
+### Prerequisites
+
+*   The **[Android Studio](https://developer.android.com/studio/index.html)** IDE. This sample has been tested on Android Studio Dolphin.
+
+*   A physical Android device with a minimum OS version of SDK 24 (Android 7.0 -
+    Nougat) with developer mode enabled. The process of enabling developer mode
+    may vary by device.
+
+### Building
+
+*   Open Android Studio. From the Welcome screen, select Open an existing
+    Android Studio project.
+
+*   From the Open File or Project window that appears, navigate to and select
+    the mediapipe/examples/gesture_recognizer/android directory. Click OK. You may
+    be asked if you trust the project. Select Trust.
+
+*   If it asks you to do a Gradle Sync, click OK.
+
+*   With your Android device connected to your computer and developer mode
+    enabled, click on the green Run arrow in Android Studio.
+
+### Models used
+
+Downloading, extraction, and placing the models into the *assets* folder is
+managed automatically by the **download.gradle** file.