[flang][NFC] Add comment.

GitOrigin-RevId: e892109c3e55eefcd197d9ef8dc701550d5f268e
diff --git a/lib/Optimizer/Dialect/FIRAttr.cpp b/lib/Optimizer/Dialect/FIRAttr.cpp
index 0a219d1..1e7a276 100644
--- a/lib/Optimizer/Dialect/FIRAttr.cpp
+++ b/lib/Optimizer/Dialect/FIRAttr.cpp
@@ -5,6 +5,10 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
+//
+// Coding style: https://mlir.llvm.org/getting_started/DeveloperGuide/
+//
+//===----------------------------------------------------------------------===//
 
 #include "flang/Optimizer/Dialect/FIRAttr.h"
 #include "flang/Optimizer/Dialect/FIRDialect.h"