[llvm] [llvm][docs] Improve usage note on stacked PRs (PR #138949)

[Paschalis Mpeis via llvm-commits]

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@@ -288,13 +288,13 @@ Your options are as follows:
    in ``llvm/llvm-project``.
 
 .. note::
-   When not using user branches, GitHub will not display proper diffs for
-   subsequent PRs in a stack. Instead, it will show a combined diff that
-   includes all commits from earlier PRs.
+   When using the dependency notes approach, GitHub will not display proper
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paschalis-mpeis wrote:

Alright, this is addressed. Given it gets accepted I'll merge by the end of this week.

Thanks Andrzej and all!

https://github.com/llvm/llvm-project/pull/138949