iPad is not showing in Develop menu on OSX Safari

Enable web inspector on your iOS device by following these steps:

iOS Device > Settings app > Safari > Advanced > Web Inspector

This setting allows you to connect to safari on your desktop.

I know this is a little late. I had this same issue and figured I would post how I got it to work in my case just in case it helps anyone in the future. I enabled it on the iPad and it didn't show. I tried closing Safari on the iPad, disconnecting and reconnecting the cable and neither worked. It ended up for me being really simple, I just quit of Safari on my laptop and restarted it and Safari then recognized the iPad and allowed me to debug. This may not work for every case but it did for me, hope it helps.

edit: just a note, I had the iPad plugged in with web inspector enabled when I restarted Safari.