Update docs and changelog

CHANGELOG.md

@@ -7,6 +7,7 @@
 - Add [raw](https://docs.imgproxy.net/latest/generating_the_url?id=raw) processing option.
 - Add [OpenTelemetry](https://docs.imgproxy.net/latest/open_telemetry) support.
 - (pro) Add encrypted source URL support.
+- (pro) Add [watermark_shadow](https://docs.imgproxy.net/generating_the_url?id=watermark-shadow) processing option.
 
 ### Changed
 - Try to fix some invalid source URL cases that happen because of URL normalization.

docs/generating_the_url.md

@@ -482,6 +482,16 @@ When `%height` is set to `0`, imgproxy will calculate the height using the defin
 
 Default: `0:0`
 
+### Watermark Shadow![pro](/assets/pro.svg) :id=watermark-shadow
+
+```
+watermark_shadow:%sigma
+wmsh:%sigma
+```
+When set, imgproxy will add a shadow to the watermark. The value of `sigma` defines the size of the mask imgproxy will use to blur the shadow.
+
+Default: disabled
+
 ### Style![pro](/assets/pro.svg) :id=style
 
 ```