Added an example ISL config file.

The ISL config file is a csv file with information about links between switches controlled by the same rfclient.
The first line is discarded.

Then each line should match the following format:
vm_id,ct_id,dp_id, dp_port, eth_addr,rem_id,rem_port,rem_eth_addr

vm_id: datapath id for rfvm
ct_id: controller id for either switch. You only have to add each link once, it's arbitrary which one you choose to add here and which one as the remote switch.
dp_id: The datapath id for the switch whose controller you added in the previous line (the first switch).
dp_port: The port on the first switch.
eth_addr: The ethernet address of ^-- that port.
rem_ct: The controller id of the other switch (the remote switch).
rem_id: The datapath id of the remote switch.
rem_port: The port on the remote switch (2).
rem_eth_addr: The address of the port on the remote switch.