docs: introduce directory layout and volumes (#271)

Author: Djaytan

docs/user-guide/src/directory-layout-and-volumes.md

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+# Directory Layout and Volumes
+
+One of the biggest advantages of this OCI image is its **clear and intentional directory layout**, designed from the ground up to make volume mounting flexible
+and straightforward for you.
+
+This isn’t just a minor detail — it’s a **core feature** of the image, just as important as the [fine-grained configuration options](configuration.md) you’ll
+rely on every day.
+
+Here’s how this layout benefits you:
+
+- ⚙️ **Manage your server configurations your way.**<br/>
+  Most needs are met with default settings or environment variables. For advanced customization, simply mount override configuration files as explained
+  in [the dedicated section](configuration-files.md).
+
+- 🌍 **Keep your worlds safe and separate.**<br/>
+  World saves are stored independently, making imports, backups, and migrations simple.
+
+- 🔌 **Handle plugins and their data cleanly.**<br/>
+  Whether adding or updating plugins, the directory layout lets you mount plugins and their data separately, keeping management natural and organized.
+
+Because these important pieces—configurations, worlds, and plugins—are each neatly separated, you can choose exactly what you want to persist or modify. This
+setup simplifies backups, migrations, and even automation, letting you keep control without extra hassle.
+
+In short: the directory layout is designed with *you* in mind, to make managing your server easier, more predictable, and flexible as your needs evolve.