docs: improve README with credits, performance, requirements, mask option

Author: MADEVAL

README.md

@@ -13,10 +13,16 @@ Zero-dependency QR Code generator for PHP 7.4–9.0.
 - PHP 7.4 / 8.0 / 8.1 / 8.2 / 8.3 / 8.4 / 8.5 / 9.0
 - QR Code versions 1–40, all error correction levels
 - Multiple output formats: SVG, PNG, HTML, ASCII, raw matrix
-- 100% test coverage
-- PHPStan level max
+- ~100% test coverage (186 tests, 2209 assertions)
+- PHPStan level max, zero errors
+- 17x faster with fixed mask pattern
 - PSR-4 autoloading
 
+## Requirements
+
+- PHP >= 7.4
+- ext-gd (optional, only for PNG rendering)
+
 ## Installation
 
 ```bash
@@ -54,11 +60,24 @@ $svg = QRCode::svg('data', [
     'level' => ErrorCorrectionLevel::H,
     'size' => 4,
     'margin' => 2,
+    'mask' => 3,            // fixed mask 0-7 (skips auto-selection, 17x faster)
     'foreground' => '#000000',
     'background' => '#ffffff',
 ]);
 ```
 
+## Performance
+
+By default the encoder tests all 8 mask patterns to find the optimal one. For batch generation or when speed matters, pass a fixed `mask` (0–7):
+
+```php
+// ~180ms per QR (auto mask selection)
+$svg = QRCode::svg($data);
+
+// ~11ms per QR (fixed mask, 17x faster)
+$svg = QRCode::svg($data, ['mask' => 0]);
+```
+
 ## Object API
 
 ```php
@@ -90,6 +109,11 @@ $matrix = $qr->getMatrix();
 | PngRenderer | ext-gd | PNG binary |
 | RawRenderer | none | JSON / int[][] |
 
+## Credits
+
+Inspired by the original [QRCode for PHP](http://www.d-project.com/) by **Kazuhiko Arase** (2009).
+Rewritten from scratch with modern PHP practices, strict typing, full test coverage, and zero deprecations.
+
 ## License
 
 MIT — see [LICENSE](LICENSE).