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

[Paschalis Mpeis via llvm-commits]

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@@ -288,16 +288,15 @@ Your options are as follows:
    in ``llvm/llvm-project``.
 
 .. note::
-   When not using user branches, GitHub will not display proper diffs for
+   When using the second approach, GitHub will not display proper diffs for
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paschalis-mpeis wrote:

I opened this PR because line [295](https://github.com/llvm/llvm-project/pull/138949/files#diff-2ffdcd91784145f84fd7eba67dacb7ef2b20ea5469917531bf119e2207f77a3dL295) was pointing to the wrong approach after my reordering. So I do see your point, and I agree.

Thanks. I've sent a new patch.

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