updated auth info for cert_name argument

Author: saurabhkothari

README.md

@@ -77,13 +77,15 @@ terraform apply -parallelism=1
       # private key path
       private_key = "path to private key"
       # Certificate Name
-      cert_name = "certificate.crt"
+      cert_name = "admin-cert"
       # cisco-aci url
       url      = "https://my-cisco-aci.com"
       insecure = true
   }
 ```
 
+Note: The value of "cert_name" arugument must match the name of the certificate attached to the APIC user (aaaUserCert) used for signature-based authentication
+
 Developing The Provider
 -----------------------
 If you want to work on the provider, you'll first need [Go](http://www.golang.org) installed on your machine. You'll also need to correctly setup a [GOPATH](http://golang.org/doc/code.html#GOPATH), as well as adding `$GOPATH/bin` to your `$PATH`.