refactor: replace custom CRM with Monica fork

docs/installation/providers/cloudron.md

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+# Installing Monica on Cloudron
+
+Monica is available as a 1-click install on [Cloudron](https://cloudron.io). For those unaware,
+Cloudron makes it easy to run web apps on your server and keep them up-to-date.
+
+[![Install](https://cloudron.io/img/button.svg)](https://cloudron.io/button.html?app=com.monicahq.cloudronapp)
+
+When you visit the app for the first time, you will be prompted to register a new account. Put in your email address
+and password and you will be logged into the app. This is the only account that has access unless you invite other people.
+
+There is a demo available at https://my.demo.cloudron.io (username: cloudron password: cloudron)
+
+# Package source
+
+The Cloudron package is developed [here](https://git.cloudron.io/cloudron/monica-app).
+