Add note about WebP support to v1.4.0-beta.1 change log

This clarifies that WebP files will only be loaded if the file extension is explicitly specified (and not when `.*` is used for the file extension). This is presumably as there is a whitelist of file extensions in the foobar2000 core.

CHANGELOG.md

@@ -15,8 +15,10 @@
 ### Features
 
 * The Windows Imaging Component is now used to load button images, and artwork in the artwork panel and playlist view.
-
-  This change adds WebP support on Windows 10 1809 and newer. (On older versions of Windows, [the Google WebP codec](https://storage.googleapis.com/downloads.webmproject.org/releases/webp/WebpCodecSetup.exe) can be installed to add WebP support.) [[#276](https://github.com/reupen/columns_ui/pull/276)]
+
+  This change adds WebP support on Windows 10 1809 and newer. (On older versions of Windows, [the Google WebP codec](https://storage.googleapis.com/downloads.webmproject.org/releases/webp/WebpCodecSetup.exe) can be installed to add WebP support.)
+
+  Note: Currently, when configuring artwork sources in Display preferences, the .webp file extension must be explicitly specified for WebP files to be loaded. (Using `.*` for the file extension will not load WebP files.) [[#276](https://github.com/reupen/columns_ui/pull/276)]
 
 ### Internal changes