Update .github/INCIDENT_RESPONSE.md

Co-authored-by: Andrew Murray <3112309+radarhere@users.noreply.github.com>

Author: aclark4life

.github/INCIDENT_RESPONSE.md

@@ -230,7 +230,7 @@ require a Pillow point release even if Pillow's own code is unchanged.
 | Library | Purpose | Security advisory tracker |
 |---|---|---|
 | [libjpeg-turbo](https://libjpeg-turbo.org/) | JPEG encode/decode | [GitHub](https://github.com/libjpeg-turbo/libjpeg-turbo/security) |
-| [libpng](http://www.libpng.org/pub/png/libpng.html) | PNG encode/decode | [SourceForge](https://sourceforge.net/p/libpng/bugs/) |
+| [libpng](http://www.libpng.org/pub/png/libpng.html) | PNG encode/decode within FreeType 2, OpenJPEG and WebP | [SourceForge](https://sourceforge.net/p/libpng/bugs/) |
 | [libtiff](https://libtiff.gitlab.io/libtiff/) | TIFF encode/decode | [GitLab](https://gitlab.com/libtiff/libtiff/-/work_items) |
 | [libwebp](https://chromium.googlesource.com/webm/libwebp) | WebP encode/decode | [Chromium tracker](https://issues.webmproject.org/issues) |
 | [libavif](https://github.com/AOMediaCodec/libavif) | AVIF encode/decode | [GitHub](https://github.com/AOMediaCodec/libavif/security) |