Bazel DevSite: Add link to 5.1.1 docs

PiperOrigin-RevId: 449201989
diff --git a/site/en/versions/_toc.yaml b/site/en/versions/_toc.yaml
index 1068b85..86b8114 100644
--- a/site/en/versions/_toc.yaml
+++ b/site/en/versions/_toc.yaml
@@ -1,4 +1,6 @@
 toc:
+- label: "5.1.1 ↗"
+  path: https://docs.bazel.build/versions/5.1.1/bazel-overview.html
 - label: "5.1 ↗"
   path: https://docs.bazel.build/versions/5.1.0/bazel-overview.html
 - label: "5.0 ↗"