Update changelog & fix typo in docs

CHANGELOG.md

@@ -1,6 +1,9 @@
 # Changelog
 
 ## [Unreleased]
+### Added
+- (pro) [video_thumbnail_second](https://docs.imgproxy.net/#/generating_the_url_advanced?id=video-thumbnail-second) processing option.
+- (pro) [background_alpha](https://docs.imgproxy.net/#/generating_the_url_advanced?id=background-alpha) processing option.
 
 ## [2.14.1] - 2020-07-22
 ### Fix

docs/generating_the_url_advanced.md

@@ -422,7 +422,7 @@ gifo:%gif_optimize_frames:%gif_optimize_transparency
 
 Allows redefining GIF saving options. All arguments have the same meaning as [Advanced GIF compression](configuration.md#advanced-gif-compression) configs. All arguments are optional and can be omitted.
 
-#### Video thumnail second <img class="pro-badge" src="assets/pro.svg" alt="pro" />
+#### Video thumbnail second <img class="pro-badge" src="assets/pro.svg" alt="pro" />
 
 ```
 video_thumbnail_second:%second