Add titles to Bazel documentation pages.

Fixes #790

--
MOS_MIGRATED_REVID=112563137
diff --git a/site/docs/cpp.md b/site/docs/cpp.md
index 7a194e0..8ae8595 100644
--- a/site/docs/cpp.md
+++ b/site/docs/cpp.md
@@ -1,5 +1,6 @@
 ---
 layout: documentation
+title: C++ Basics
 ---
 
 C++ Basics