Docs: Add instructions to configure data_dir on Linux

docs/content/reference/data_directory.md

@@ -16,3 +16,30 @@ configuration files, etc.
 
 On Linux, the default path is `$HOME/.monkey_island`.
 On Windows, the default path is `%AppData%\monkey_island`.
+
+## How do I configure the location of the data directory on Linux?
+
+The location of the data directory is set in the `data_dir` field in the
+`server_config.json` file.
+
+1. Create a custom `server_config.json` file and set the `data_dir` field. Its
+   contents will look like:
+
+    ```json
+    {
+      "log_level": "DEBUG",
+      "environment": {
+        "server_config": "password"
+      },
+      "mongodb": {
+            "start_mongodb": true
+      },
+      "data_dir": "<PATH_TO_DATA_DIR>"
+    }
+    ```
+
+1. Start the Infection Monkey with the `--server-config` parameter.
+
+    ```bash
+    $ InfectionMonkey-VERSION.AppImage --server-config <PATH_TO_SERVER_CONFIG>
+    ```