Add more documentation to release automation

There is a script available for automatic setup, which is helpful if you want to replicate this on

your own repository for devlopment. Please see /scripts/setup_release_automation.

You can run it using:

```bash

python -m venv venv

source venv/bin/activate

pip install requests pynacl

cd .signing

python ../scripts/setup_release_automation -r yourfork/thunderbird-android

```

You will need the following files:

- The signing keys with their default filenames

- A matrix-account.json with the following keys:

```

{

  "homeserver": "matrix-client.matrix.org",

  "room": "room id here",

  "token": "matrix token here",

  "userMap": {

    "github_username": "@matrix_id:mozilla.org"

  }

}

```

- `play-store-account.json` with the service account json that will do the uploads

- `thunderbird-mobile-gh-releaser-bot.clientid.txt` as a simple file with the client ID of the releaser bot (you can skip this to use GitHub Actions as the user)

- `thunderbird-mobile-gh-releaser-bot.pem` with the private key of the releaser bot

## Build Environments

Build environments determine the configuration for the respective release channel. The following are

    "packageFormat": "bundle",

    "packageFlavor": "full"

  },

  { "appName": "k9mail", "packageFormat": "apk" }

  { "appName": "k9mail", "packageFormat": "apk", "packageFlavor": "foss" }

]

```

    <appName>_<releaseType>_<packageFlavor>

    thunderbird_beta_full

    thunderbird_beta_foss

    k9mail_beta_default

    k9mail_beta_foss

The following secrets are needed:

- RELEASER_APP_PRIVATE_KEY: Secret with the private key of the app

The releases environment is locked to the release, beta and main branches.

If you leave out the environment, the Github Actions user will be used.

## Matrix Notify Environment

This environment will notify about build updates. It requires the following keys:

- MATRIX_NOTIFY_TOKEN: The Matrix token of the user

- MATRIX_NOTIFY_HOMESERVER: The homeserver for the account

- MATRIX_NOTIFY_ROOM: The room id to notify in

- MATRIX_NOTIFY_USER_MAP: A json object that maps github usernames to matrix ids

If you leave out this environment, no notifications will be sent.

# See docs/CI/Release_Automation.md for more details

# Run this from the .signing directory with all the keys and properties files in it.

# python -m venv venv; source venv/bin/activate; pip install requests, pynacl

# python -m venv venv; source venv/bin/activate; pip install requests pynacl

import os

import json