Add small doc on Mautrix Telegram

docs/configuring-playbook-bridge-mautrix-telegram.md

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+# Setting up Mautrix Telegram
+
+The playbook can install and configure [mautrix-telegram](https://github.com/tulir/mautrix-telegram) for you.
+
+See that project's [documentation](https://github.com/tulir/mautrix-telegram/wiki#usage) to learn what it does and why it might be useful to you.