frustrating customers listings social media

Ok so what nearly every customer making a listing is doing is this:

Where it says

Twitter:

Facebook:

to be able to put a link to your twitter or Facebook, they’re just putting their social media names like “@whoever” instead of http://www.twitter.com/whoever instead of a URL to their pages.

this is taking ages for me to go through and replace everyones social media names with a link.

So, an idea to stop this….

is there anyway that in the space where you type the link, could there be a greyed out “http://www.” so people realise they’re supposed to type the whole url in there? rather than just their social media name? or maybe pre-filled in

(see screenshot example attached)

so they understand its supposed to be a url not just their name

thanks

David