Clarify use of Cookies in programmatic headers

[RobertJCarroll]

The language around using the cookies is potentially confusing as both the HTTP Request header AND Cookies use key-value pairs. Original comment:

On both of the KF and the INCLUDE instructions, “The “key” is AWSELBAuthSessionCookie-0 and the “value” is what you recorded previously.” may mislead. When you set this to the HTTP header, the key should be "Cookie" and the value should be "AWSELBAuthSessionCookie-0=". So, the header should look like: header = { "Cookie": "AWSELBAuthSessionCookie-0=<the value you copied>" }