Add docs

docs/README.md

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+# mailcow: dockerized - 🐮 + 🐋 = 💕
+
+[![Donate](https://img.shields.io/badge/Donate-PayPal-green.svg)](https://www.paypal.com/cgi-bin/webscr?cmd=_s-xclick&hosted_button_id=JWBSYHF4SMC68)
+
+Please see the official documentation for instructions => [mailcow.email/dockerized](https://mailcow.email/dockerized)