Add clarifying/instructive header to TARGETS and defs.bzl

Summary: Pull Request resolved: https://github.com/facebook/rocksdb/pull/6008

Differential Revision: D18343273

Pulled By: pdillinger

fbshipit-source-id: f7d1c78d711bbfb0deea9ec88212c19ab2ec91b8

TARGETS

+# This file @generated by `python buckifier/buckify_rocksdb.py`
+# --> DO NOT EDIT MANUALLY <--
+# This file is a Facebook-specific integration for buck builds, so can
+# only be validated by Facebook employees.
+#
 load("@fbcode_macros//build_defs:auto_headers.bzl", "AutoHeaders")
 load("@fbcode_macros//build_defs:cpp_library.bzl", "cpp_library")
 load(":defs.bzl", "test_binary")

buckifier/targets_cfg.py

@@ -3,7 +3,13 @@ from __future__ import absolute_import
 from __future__ import division
 from __future__ import print_function
 from __future__ import unicode_literals
-rocksdb_target_header = """load("@fbcode_macros//build_defs:auto_headers.bzl", "AutoHeaders")
+
+rocksdb_target_header = """# This file \100generated by `python buckifier/buckify_rocksdb.py`
+# --> DO NOT EDIT MANUALLY <--
+# This file is a Facebook-specific integration for buck builds, so can
+# only be validated by Facebook employees.
+#
+load("@fbcode_macros//build_defs:auto_headers.bzl", "AutoHeaders")
 load("@fbcode_macros//build_defs:cpp_library.bzl", "cpp_library")
 load(":defs.bzl", "test_binary")
 

defs.bzl

 # Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
+#
+# defs.bzl - Definitions for Facebook-specific buck build integration
+# in TARGETS
 
 load("@fbcode_macros//build_defs:cpp_binary.bzl", "cpp_binary")
 load("@fbcode_macros//build_defs:custom_unittest.bzl", "custom_unittest")