mention using 3rd root chain file for AWS ELB.

README.md

@@ -22,6 +22,9 @@ $ openssl req -noout -text -in foobar.stanford.edu.csr
 
 ## Upload cert to AWS IAM service
 
+Make sure `foo_stanford_edu_cert.cer` and `foo_stanford_edu_interm.cer` are in the current directory. The foo_stanford_edu_interm.cer should be the reverse 
+order root chain file (3rd from certs you download from InCommon) for AWS. 
+
 ```
 ./upload_cert_to_aws.sh -s foo.stanford.edu -p foo.stanford.edu
 ```