Update references to mailing lists that have moved to Discourse.

GitOrigin-RevId: 520d29f38108e60bff3f10ffec9443745e3217c5
diff --git a/docs/index.rst b/docs/index.rst
index a831529..7126d02 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -96,7 +96,7 @@
 ===========
 * `LLVM Homepage <https://llvm.org/>`_
 * `LLVM Bug Tracker <https://github.com/llvm/llvm-project/labels/libunwind/>`_
-* `cfe-dev Mailing List <http://lists.llvm.org/mailman/listinfo/cfe-dev>`_
+* `Clang Discourse Forums <https://discourse.llvm.org/c/clang/6>`_
 * `cfe-commits Mailing List <http://lists.llvm.org/mailman/listinfo/cfe-commits>`_
 * `Runtimes Forum <https://discourse.llvm.org/tags/c/runtimes>`_
 * `Browse libunwind Sources <https://github.com/llvm/llvm-project/blob/main/libunwind/>`_