[llvm] [libc] Updated GettingStarted.rst with PyYAML version (PR #100649)

[via llvm-commits]

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@@ -295,6 +295,7 @@ Package                                                     Version      Notes
 `python <http://www.python.org/>`_                          >=3.8        Automated test suite\ :sup:`1`
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lntue wrote:

SGTM

https://github.com/llvm/llvm-project/pull/100649