Added info about regenerating files to Makefile and BUILD templates

templates/BUILD.template

@@ -2,6 +2,8 @@
 # This currently builds C and C++ code.
 # This file has been automatically generated from a template file.
 # Please look at the templates directory instead.
+# This file can be regenerated from the template by running
+# tools/buildgen/generate_projects.sh
 
 # Copyright 2015, Google Inc.
 # All rights reserved.

templates/Makefile.template

@@ -2,6 +2,8 @@
 # This currently builds C and C++ code.
 # This file has been automatically generated from a template file.
 # Please look at the templates directory instead.
+# This file can be regenerated from the template by running
+# tools/buildgen/generate_projects.sh
 
 # Copyright 2015, Google Inc.
 # All rights reserved.