[llvm] [docs] Stress out the branch naming scheme for Graphite. (PR #104499)

[Mircea Trofin via llvm-commits]

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@@ -23,6 +23,23 @@ intended to be able to support "stacked" pull-request. Do not create any branche
 llvm/llvm-project repository otherwise, please use a fork (see below). User branches that
 aren't associated with a pull-request **will be deleted**.
 
+Using Graphite for stacked Pull Requests
+========================================
+
+[Graphite](https://app.graphite.dev/) is a stacked pull request tool supported
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mtrofin wrote:

Fixed in 62601250786244981026164b21f553c9c40a4602

https://github.com/llvm/llvm-project/pull/104499