Update changelog and docs

CHANGELOG.md

@@ -5,7 +5,8 @@
 - Better handling if non-sRGB images;
 - `SO_REUSEPORT` socker option support. Can be enabled with `IMGPROXY_SO_REUSEPORT`;
 - `dpr` option always changes the resulting size even if it leads to enlarge and `enlarge` is falsey;
-- Log to STDOUT
+- Log to STDOUT;
+- [filename](./docs/generating_the_url_advanced.md#filename) option.
 
 ## v2.3.0
 

docs/generating_the_url_advanced.md

@@ -261,6 +261,17 @@ It's highly recommended to prefer `cachebuster` option over URL query string bec
 
 Default: empty
 
+##### Filename
+
+```
+filenale:%string
+fn:%string
+```
+
+Defines a filename for `Content-Disposition` header. When not specified, imgproxy will get filename from the source url.
+
+Default: empty
+
 ##### Format
 
 ```