Add documentation for Flipper

docs/flipper.md

@@ -1,7 +1,57 @@
 # Flipper
 
-TODO Write doc
-- Setup env
-- Debug activity
->adb shell am start -n im.vector.app.debug/com.facebook.flipper.android.diagnostics.FlipperDiagnosticActivity
+<!--- TOC -->
 
+* [Introduction](#introduction)
+* [Setup](#setup)
+  * [Troubleshoot](#troubleshoot)
+    * [No device found issue](#no-device-found-issue)
+    * [Diagnostic Activity](#diagnostic-activity)
+    * [Other](#other)
+* [Links](#links)
+
+<!--- END -->
+
+## Introduction
+
+[Flipper](https://fbflipper.com) is a powerful tool from Meta, which allow to inspect the running application details and states from your computer.
+
+Flipper is configured in the Element Android project to let the developers be able to:
+- inspect all the Realm databases content;
+- do layout inspection;
+- see the crash logs;
+- see the logcat;
+- see all the network requests;
+- see all the SharedPreferences;
+- take screenshots and record videos of the device;
+- and more!
+
+## Setup
+
+- Install Flipper on your computer. Follow instructions here: https://fbflipper.com/docs/getting-started/index/
+- Run the debug version of Element on an emulator or on a real device.
+
+### Troubleshoot
+
+#### No device found issue
+
+The configuration of the Flipper application has to be updated. The issue has been asked and answered here: https://stackoverflow.com/questions/71744103/android-emulator-unable-to-connect-to-flipper/72608113#72608113
+
+#### Diagnostic Activity
+
+Flipper comes with a Diagnostic Activity that you can start from command line using:
+
+```shell
+adb shell am start -n im.vector.app.debug/com.facebook.flipper.android.diagnostics.FlipperDiagnosticActivity
+```
+
+It provides some log which can help to figure out what's going on client side.
+
+#### Other
+
+https://fbflipper.com/docs/getting-started/troubleshooting/android/ may help.
+
+## Links
+
+- https://fbflipper.com
+- Realm Plugin for Flipper: https://github.com/kamgurgul/Flipper-Realm