Add some first docs for sharpen images

More to follow with 4.1.1 when `$file->sharpen()` is added

Author: distantnative

content/docs/1_guide/5_files/3_resize-images-on-the-fly/guide.txt

@@ -27,6 +27,7 @@ With the thumb method, you can perform multiple image manipulations at once: res
         'format'    => 'webp',
         'grayscale' => true,
         'blur'      => 300,
+				'sharpen'   => 50,
         'quality'   => 70,
     ]
 )->url() ?>" alt="">

content/docs/3_reference/4_objects/cms/0_file/0_thumb/reference-classmethod.txt

@@ -26,6 +26,7 @@ $options = [
   'grayscale'  => false,
   'height'     => null,
   'quality'    => 90,
+	'sharpen'    => false,
   'width'      => null,
 ];
 ```