refactor: replace custom CRM with Monica fork

docs/user/readme.md

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+# Use Monica <!-- omit in toc -->
+
+Monica is a personal relationship manager platform.
+It helps you organize the social interactions with your loved ones.
+
+You can use a bunch of nice [features](https://www.monicahq.com/features), or use our [API](https://www.monicahq.com/api).
+See the recent [changelog](https://www.monicahq.com/changelog) to track every changes with it.
+
+See documentations about:
+
+- [Setup your phone, or desktop app to sync contacts](carddav.md)
+- [Enhance security of your account](security.md)