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

[Alexey Bader 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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bader wrote:

I suggest we use Markdown, which is de-facto standard format for the documentation on GitHub. SYCL project documentation in downstream repository uses Markdown format as well.

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