Christoph Rumpel has a tutorial posted on his site showing how to create a Telegram group bot using a bit of PHP and the BotMan library.

Working with Facebook Messengers bots is great, but there is one thing still missing: group bots! This is why we will built a little Telegram bot today and use it inside my FantasticBurger group.

First thing to keep in mind here is that a group chatbot can be very different from a 1:1 conversation chatbot. In groups chatbots are often not a direct conversation partner but more a quiet assistant.

He briefly talks about why he created the bot and how to go and set up your own Telegraph bot with a simple first command. He then walks through the set up of the BotMan library and connecting it back to the Telegraph service (via an API call) and a simple handler that returns a "Hi there" message when the bot hears the string "Hello".