[llvm] [docs] Mention ffmpeg and dav1d in llvm-test-suite (PR #120570)

[Martin Storsjö via llvm-commits]

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@@ -367,6 +367,18 @@ For the SPEC benchmarks you can switch between the `test`, `train` and
 `ref` input datasets via the `TEST_SUITE_RUN_TYPE` configuration option.
 The `train` dataset is used by default.
 
+In addition to SPEC, the multimedia frameworks ffmpeg and dav1d can also
+be hooked up as external projects in the same way. Adding them doesn't
+add the respective projects' full testsuites though. But by including
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mstorsjo wrote:

Good points, thanks. Yes, it reads much better if we start out by telling you what you get from it, rather than telling you what you don't; I rewrote it in such an order now.

https://github.com/llvm/llvm-project/pull/120570