I've created a hidden form field with the Zoho web form that I've created for the Google AdWords GCLID field and added the necessary code to the website from Google to enable offline conversion tracking. 

I've created a custom field in the lead module called gclid_field (the same as it is on the form), but when testing out things - going to example.com/?gclid=test or example.com/?gclid=TeSter123, the gclid is not showing up in the the leads module (and for some reason, I'm not actually even getting an email lead notification... I guess that's another issue).