Was setting up script, sendmytip.sh, to update PoolTool with tip and height information.

I noticed this `NODE_ID` value:

    #!/usr/bin/env bash
    
    ## CHANGE THESE TO SUITE YOUR POOL
    
    # your pool id as on the explorer
    PT_MY_POOL_ID="xxxx"
    # get this from your account profile page on pooltool website
    PT_MY_API_KEY="xxxx-xx-xx-xx-xxxx"
    # Your node ID (optional, this is reserved for future use and is not captured yet)
    PT_MY_NODE_ID="xxxx-xxx-xxx-xxx-xxxx"

It's the last line, and is clearly different from the Pool ID. 

Would anyone care to let me know how to find a node id, or explain what they are?