Added documentation for custom repos and exporter plugin

docs/Writerside/topics/IFileService.md

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+# IFileService
+
+The `IFileService` interface provides methods for handling file operations, such as downloading and uploading files within the HopFrame web application. It abstracts file-related operations to ensure a smooth and consistent user experience.
+
+## Methods
+
+1. **DownloadFile**
+    - Initiates the download of a file with the given name and data.
+    - Suitable for dynamically generating and offering files to the user, such as CSV exports or reports.
+
+   ```c#
+   Task DownloadFile(string name, byte[] data);
+   ```
+
+    - **Parameters:**
+        - `name`: The name of the file to be downloaded (including the extension, e.g., "example.csv").
+        - `data`: The byte array representing the content of the file.
+    - **Usage Example:** Exporting table data as a CSV file for download.
+
+2. **UploadFile**
+    - Allows the user to upload a file through the web interface and returns the uploaded file for further processing.
+    - This method provides integration with Blazor's `IBrowserFile` for easy file handling.
+
+   ```c#
+   Task<IBrowserFile> UploadFile();
+   ```
+
+    - **Returns:** An `IBrowserFile` instance representing the uploaded file.
+    - **Usage Example:** Importing data from a CSV file to populate or update a table.
+
+## Integration
+
+The `IFileService` is commonly used in conjunction with plugins or components that require file operations, such as the Exporter Plugin, which leverages this service to enable data export and import functionality.
+
+## Key Features
+
+- Streamlines file handling for web applications.
+- Simplifies both download and upload processes with minimal code.
+- Ensures compatibility with Blazor's file-handling capabilities.
+
+By implementing or extending the `IFileService`, developers can customize the file-handling behavior to suit specific application needs. Let me know if you'd like more examples or details!