Cleanup example program in Flag docs.

Flag.h

@@ -92,6 +92,7 @@ Flag	*NewFlag(std::string fName, FlagType fType, std::string fDescription);
 ///
 /// A short example program is below:
 ///
+/// ```c++
 /// int
 /// main(int argc, char *argv[])
 /// {
@@ -127,6 +128,7 @@ Flag	*NewFlag(std::string fName, FlagType fType, std::string fDescription);
 /// 	}
 /// 	return 0;
 /// }
+/// ```
 ///
 class Flags {
 public: