[libcxx] Add Maintainers.md file

Author: DavidSpickett

libcxx/Maintainers.md

@@ -0,0 +1,10 @@
+# libc++ Maintainers
+
+This file is a list of the
+[maintainers](https://llvm.org/docs/DeveloperPolicy.html#maintainers) for
+libc++.
+
+# Lead maintainer
+
+Louis Dionne \
+[email protected] (email), [ldionne](https://github.com/ldionne) (GitHub)

llvm/Maintainers.md

@@ -434,17 +434,14 @@ Others only have a lead maintainer listed here.
 
 [Flang maintainers](https://github.com/llvm/llvm-project/blob/main/flang/Maintainers.txt)
 
+[libc++ maintainers](https://github.com/llvm/llvm-project/blob/main/libcxx/Maintainers.md)
+
 [LLD maintainers](https://github.com/llvm/llvm-project/blob/main/lld/Maintainers.md)
 
 [LLDB maintainers](https://github.com/llvm/llvm-project/blob/main/lldb/Maintainers.rst)
 
 [LLVM OpenMP Library maintainers](https://github.com/llvm/llvm-project/blob/main/openmp/Maintainers.md)
 
-#### libc++
-
-Louis Dionne \
-[email protected] (email), [ldionne](https://github.com/ldionne) (GitHub)
-
 #### libclc
 
 Tom Stellard \