[llvm] [libsycl] Add Maintainers.rst file (PR #168550)

[Kseniya Tikhomirova via llvm-commits]

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@@ -511,6 +511,8 @@ Some subprojects maintain their own list of per-component maintainers.
 
 [libclc maintainers](https://github.com/llvm/llvm-project/blob/main/libclc/Maintainers.md)
 
+[libsycl maintainers](https://github.com/llvm/llvm-project/blob/main/libsycl/Maintainers.rst)
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KseniyaTikhomirova wrote:

"Suitable reviewers are the maintainers of the project you are modifying, and
anyone else working in the area your patch touches. To find maintainers, look for
the ``Maintainers.md`` or ``Maintainers.rst`` file in the root of the project's
sub-directory. For example, LLVM's is ``llvm/Maintainers.md`` and Clang's is
``clang/Maintainers.rst``."
from https://github.com/llvm/llvm-project/blob/main/llvm/docs/Contributing.rst

I believe both options are valid.

https://github.com/llvm/llvm-project/pull/168550