add headers curl code example

Example 1: curl headers

# -i to include response headers in the output.
# -H to specify a header
# -X to specify the request method
curl -i -H "Accept: application/json" -H "Content-Type: application/json" -X GET http://hostname/resource

Example 2: curl host header

curl --header "Host: example.com" http://127.0.0.1/