docs(pgadmin): system_stats postgres extension

doc/pgadmin.md

@@ -16,3 +16,34 @@
   };
 }
 ```
+
+## Guide
+
+### Visualize system statistics
+
+`pgAdmin` uses the functions exposed by [system_stats](https://github.com/EnterpriseDB/system_stats) [[postgresql]] extension to monitor the system metrics such as CPU, memory and disk information. Use this in your config:
+
+```nix
+# In `perSystem.process-compose.<name>`
+{
+  services.postgres."pg1" = {
+    enable = true;
+    extensions = exts: [
+      exts.system_stats
+    ];
+    # This creates the extensions for the `postgres` database, if you need it for a custom database,
+    # ensure to add the below script in `schemas` of the database of your choice under `initialDatabses`.
+    initialScript.before = ''
+      CREATE EXTENSION system_stats;
+    '';
+  };
+  services.pgadmin."pgad1" = {
+    enable = true;
+    initialEmail = "[email protected]";
+    initialPassword = "password";
+  };
+}
+```
+
+Open the pgAdmin dashboard, establish a connection with your database and you will see:
+![[pgadmin-system-stats.png]]