Dev-Dep guide: mention AST third party requirements

Avoid the likes of:

```
Error:
ActiveStorage::RepresentationTest#test_representing_an_MP4_video:
Errno::ENOENT: No such file or directory - ffmpeg
    test/models/representation_test.rb:27:in `block in <class:RepresentationTest>'
```

Also note additiona macOS requirements in ActiveStorage guide.

[ci skip]

1 files changed, 5 insertions, 5 deletions

diff --git a/guides/source/active_storage_overview.md b/guides/source/active_storage_overview.md
index cb9acdadcf..3b7c23f2af 100644
--- a/guides/source/active_storage_overview.md
+++ b/guides/source/active_storage_overview.md
@@ -446,11 +446,11 @@ the box, Active Storage supports previewing videos and PDF documents.
 </ul>
 ```
 
-WARNING: Extracting previews requires third-party applications, `ffmpeg` for
-video and `mutool` for PDFs. These libraries are not provided by Rails. You must
-install them yourself to use the built-in previewers. Before you install and use
-third-party software, make sure you understand the licensing implications of
-doing so.
+WARNING: Extracting previews requires third-party applications, `FFmpeg` for
+video and `muPDF` for PDFs, and on macOS also `XQuartz` and `Poppler`.
+These libraries are not provided by Rails. You must install them yourself to
+use the built-in previewers. Before you install and use third-party software,
+make sure you understand the licensing implications of doing so.
 
 Direct Uploads
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