Add sysadmin roadmap

content/roadmaps/7-postgresql-dba/resources.md

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+> **We are still preparing the resources**. Please check back later or [subscribe to get notified](/signup).
+
+While we prepare the list, follow this simple advice to learn anything
+ 
+> Just **pick a project and start working on it**, you will learn all that you need along the way.
+
+**→**   [All Roadmaps](/roadmaps)  •  [Programming guides](/guides)  •  [Subscribe](/signup)