Mention OpenBSD in the documentation

NOKEYCHECK=True
GitOrigin-RevId: 3fa4cff97480e47fad77e54b287061c492ab9ea8
diff --git a/docs/UsingLibcxx.rst b/docs/UsingLibcxx.rst
index 8631236..f37e23b 100644
--- a/docs/UsingLibcxx.rst
+++ b/docs/UsingLibcxx.rst
@@ -68,8 +68,8 @@
 
   $ clang++ -stdlib=libc++ test.cpp
 
-On systems where libc++ is the library in use by default such as macOS and FreeBSD,
-this flag is not required.
+On systems where libc++ is the library in use by default such as macOS, FreeBSD
+and OpenBSD, this flag is not required.
 
 
 .. _alternate libcxx: