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

[Andrzej Warzyński 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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banach-space wrote:

I would prefer some clearer/unambiguous way to refer to the approaches above. To me:
* `not using user branches` is clearer than
* `the dependency notes approach`.

Primarily because we have a dedicated paragraph on `user branches`.  But that might simply be my bias. If you like `dependency notes` then I suggest:
* `dependency notes` -> `"dependency note"` (use quotes to signal that it's some "custom" thing defined in this document + use singular as we are only asking for one note in the 2nd paragraph above).

Hope this makes sense :)  

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