add missing comma in cc_library example

Closes #5758.

PiperOrigin-RevId: 208203915
diff --git a/site/docs/cpp-use-cases.md b/site/docs/cpp-use-cases.md
index 04d6920..4844902 100644
--- a/site/docs/cpp-use-cases.md
+++ b/site/docs/cpp-use-cases.md
@@ -29,7 +29,7 @@
 ```python
 cc_library(
     name = "build-all-the-files",
-    srcs = glob(["*.cc"])
+    srcs = glob(["*.cc"]),
     hdrs = glob(["*.h"]),
 )
 ```