[llvm] [llvm][docs] Extend docs on GitHub's "squash and merge" (PR #129497)

[David Spickett via llvm-commits]

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@@ -15,6 +15,12 @@ The LLVM Project uses `GitHub <https://github.com/>`_ for
 This page describes how the LLVM Project users and developers can
 participate in the project using GitHub.
 
+Before your first PR
+====================
+
+Please ensure that you have set a valid email address in your GitHub account,
+see :ref:`github-email-address`.
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DavidSpickett wrote:

FYI this links to https://llvm.org/docs/DeveloperPolicy.html#github-email-address, would having read that change your opinion here?

https://github.com/llvm/llvm-project/pull/129497