Add documentation and small script to test external deep links.

Author: bmarty

docs/deeplink.md

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+# Element X Android deeplink
+
+<!--- TOC -->
+
+* [Introduction](#introduction)
+  * [Asset Links](#asset-links)
+  * [Supported links](#supported-links)
+* [Developer tools](#developer-tools)
+
+<!--- END -->
+
+
+## Introduction
+
+Element X Android supports deep linking to specific screens in the application. This document explains how to use deep links in Element X Android.
+
+### Asset Links
+
+The asset links file is available at https://element.io/.well-known/assetlinks.json
+
+### Supported links
+
+Element Call link: 
+> https://call.element.io/Example
+
+Link to a user:
+> https://app.element.io/#/user/@alice:matrix.org
+
+Link to a room by id or alias:
+> https://app.element.io/#/room/!roomid:matrix.org
+> https://app.element.io/#/room/#element-x-android:matrix.org
+
+Link to a room with a specific event:
+> https://app.element.io/#/room/!roomid:matrix.org/$eventid
+
+Note that it will also work with other domain such as:
+> https://mobile.element.io
+> https://develop.element.io
+> https://staging.element.io
+
+## Developer tools
+
+Using an Android 12 or higher emulator
+
+Ensure links verification is enabled
+```bash
+adb shell am compat enable 175408749 io.element.android.x.debug  
+```
+
+Reset link verifications for the given package id
+```bash
+adb shell pm set-app-links --package io.element.android.x.debug 0 all 
+```
+
+Force the package id links to be verified
+```bash
+adb shell pm verify-app-links --re-verify io.element.android.x.debug 
+```
+
+Print the link verification of the package id
+```bash
+adb shell pm get-app-links io.element.android.x.debug
+```
+
+```
+  io.element.android.x.debug:
+    ID: e2ece472-c266-4bf0-829c-be79959a6270
+    Signatures: [B0:B0:51:DC:56:5C:81:2F:E1:7F:6F:3E:94:5B:4D:79:04:71:23:AB:0D:A6:12:86:76:9E:B2:94:91:97:13:0E]
+    Domain verification state:
+      *.element.io: 1024
+```

tools/adb/deeplink_external.sh

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+#! /bin/bash
+#
+# Copyright (c) 2024 New Vector Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+adb shell am start -a android.intent.action.VIEW -c android.intent.category.BROWSABLE \
+   -d "https://app.element.io/#/room/!cuqHozLHNBgupgLMKN:matrix.org/%24LZDOueY3R8OD2ZYf8FLKtu95aF7imLBC3F5TIUj-4cc"