Add clarification notes on configuration parameter usage

[jjzazuet]

In relation to #47, I just wanted to contribute a few bits of documentation which might help users figure out whay are they not getting Telegram notifications. The way to determine a chat group id comes from this StackOverflow answer.

Hope this helps. Thanks.

PLUGIN_TOKEN and PLUGIN_TO parameter configuration.

• PLUGIN_TOKEN is the token issued by @BotFather when configuring a new bot, as described in Telegram's Bot API.

• PLUGIN_TO consist of a numerical id, which specifies the Telegram chat group where the Telegram plugin will send build notifications. To obtain the chat group id:

• Call the telegram API using your bot's token:

  https://api.telegram.org/bot<THE_BOT_TOKEN>/getUpdates

And extract the id value from the chat object in the JSON response.

{
  "ok": true,
  "result": [{
    "update_id": 549000058,
    "message": {
      "message_id": 3,
      "from": {
        "id": 000000000,
        "is_bot": false,
        "first_name": "AHumansFirstName",
        "last_name": "AHumansLastName",
        "username": "humanUsername",
        "language_code": "en"
      },
      "chat": {
        "id": 123456789,
        "first_name": "AHumansFirstName",
        "last_name": "AHumansLastName",
        "username": "humanUsername",
        "type": "private"
      },
      "date": 1513466390,
      "text": "LOLZ"
    }
  }]
}