Add features and layout customization options and update README documentation

This commit adds several new layout customization features to the QR code label generator:

- Added support for vertical and horizontal offset in mm to shift the entire label grid
- Added adjustable label height (in mm) for better compatibility with various printers
- Added content scale (%), allowing QR code and text size to be fine-tuned
- Introduced a "Show Border" toggle to display label borders for alignment and calibration

These options allow precise tuning of the print layout for Avery L4731REV-25 sheets, improving print accuracy across different printers and paper feeds.

The README file was also updated to reflect the new functionality under the "Features" section, and the overall project description was improved for clarity.

README.md

@@ -17,6 +17,18 @@ The application currently supports the following label formats:
 
 - Avery L4731REV-25 (See [UK shop](https://www.avery.co.uk/product/mini-multipurpose-labels-l4731rev-25), [DE shop](https://www.avery-zweckform.com/produkt/universal-etiketten-l4731rev-25))
 
+### Features
+
+- Generate up to 189 QR code labels in a batch
+- Customize start number, prefix, and number formatting
+- Adjustable layout options for precise printer alignment:
+  - Vertical Offset (mm): shifts the label grid up or down
+  - Horizontal Offset (mm): shifts the label grid left or right
+  - Label Height (mm): controls the vertical size of each label
+  - Content Scale (%): scales QR code and text inside each label
+  - Show Border: toggles visible borders to help with calibration
+- Print-ready formatting for A4 label sheets
+
 ### Limitations
 
 The application currently has the following limitations: