Created Introduction to the API (markdown)

Introduction-to-the-API.md

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+The API is exposed via the `telegram.Bot` class. The methods have names as described in the official [Telegram Bot API](https://core.telegram.org/bots/api), but equivalent snake_case methods are available for [PEP8](https://www.python.org/dev/peps/pep-0008/) enthusiasts. So for example `telegram.Bot.send_message` is the same as `telegram.Bot.sendMessage`.
+
+To generate an Access Token, you have to talk to [BotFather](https://telegram.me/botfather) and follow a few simple steps (described [here](https://core.telegram.org/bots#6-botfather)).
+
+For full details see the [Bots: An introduction for developers](https://core.telegram.org/bots).
+
+#### The first API call
+
+To get a feeling for the API and how to speak to it with `python-telegram-bot`, please open a Python command line and follow the next few steps.
+
+First, create an instance of the `telegram.Bot`. `'TOKEN'` should be replaced by the API token you received from `@BotFather`:
+
+```python
+>>> import telegram
+>>> bot = telegram.Bot(token='TOKEN')
+```
+
+To check if your credentials are correct, call the [getMe](https://core.telegram.org/bots/api#getme) API method:
+
+```python
+>>> print(bot.getMe())
+{"first_name": "Toledo's Palace Bot", "username": "ToledosPalaceBot"}
+```
+
+**Note:** Bots can't initiate conversations with users. A user must either add them to a group or send them a message first. People can use ``telegram.me/<bot_username>`` links or username search to find your bot.
+
+#### What to read next?
+If you want to continue learning about the API, read [Code snippets]().
+
+To get real and start building your first bot using the `telegram.ext` classes, read [Extensions]()